KINE 451: Weight Management for Athletes

Welcome back to our online sport nutrition lecture series. Today's topic is going to be weight management for athletes. Perhaps the most common issue in weight management for athletes is maintaining optimal body weights, but also, more importantly, body compositions in order to improve their performance.

Many athletes face the need to lose weight or attempt to lose weight, specifically body fat, even if they're at a healthy weight for several reasons. Those reasons, uh, could be to improve their power to body weight ratio. So, this could be particularly important in sports where jumping is an integral part of performance. They may want to reduce the amount of energy that it costs to perform a given activity. This is prevalent in endurance athletes, for sure. In some sports, athletes need to make a certain weight category in order to be eligible to compete, such as wrestling, judo, boxing, and even Olympic weightlifting. And then, of course, there's this expectation of a lean aesthetic in many sports. Um, ballet would be considered one where the aesthetic component of performance, um, is meant to elude an artistic effect. But this is also true in sports where judging is a part of, um, of success, such as gymnastics and, and figure skating.

And if we think about weight loss and the common goal of weight loss in athletes, it's not always a good idea. While losing body fat may improve performance via one or more of the reasons that we just discussed, the reduction in weight oftentimes comes at the expense of lean mass. So, while athletes may lose, lose fat, they may also lose some of their functional mass and reduce their muscle mass. Additionally, because of some of the restrictive diet practices that athletes undertake to make weight, they may also reduce their stored carbohydrate. They may, they may experience chronic levels of fatigue and increase their risk for injury during performance when they are following, um, restrictive eating practices. And then, of course, from a psychological standpoint, the continued practice of restrictive eating and weight loss, uh, definitely increases the risk of developing eating disorders such as anorexia or bulimia, which can be a major issue that can cause problems such as the female athlete triad.

So, if we think about best methods for either maintaining weight, gaining weight, or losing weight, we know that one of the classic approaches, or perhaps the most well-understood factor in weight management, is going to be the concept of energy balance. So, the simple concept of whether food intake and energy expenditure are equal to each other, resulting in the maintenance of weight; whether food intake exceeds, um, energy expenditure, creating a positive energy balance and weight gain, which may be a desirable outcome for some athletes, and we'll talk about that later in the presentation; and then, of course, the negative energy balance that is thought to be required for, for weight loss, where total energy expenditure is exceeding that, um, of energy being in taken, resulting in a negative energy balance.

But the question is, is it really just that simple? Should we just recommend that when athletes want to, want to lose weight, that they just eat less and do more physical activity or train more, or vice versa in the case where they want to gain weight? Now, while I'm about to make the argument that it's not as simple as just energy in and energy out, I want to start by saying that that is certainly the primary component of any weight maintenance strategy. Whether it is to gain or lose weight, a negative or positive energy balance is going to be the very first prerequisite for that to occur.

But this is confounded by the fact that we know when, when you lose weight or you decrease your body mass, you also decrease your resting metabolic rate, or the number of calories needed, needed to maintain healthy function as a result of that decrease in body mass. And this makes losing weight for athletes and keeping it off even more difficult. And it's even further confounded if a significant amount of that weight is lean mass, given that we mass is metabolically active tissue.

The same thing would be true in terms of what happens when weight is gained. When you increase your body mass, you increase that resting energy costs, and this makes gaining weight for athletes and keeping it on more difficult long term, especially again, if a good proportion of that weight that is gained is in favor of lean body mass and muscle.

So, in efforts to lose weight, if we look at some of the common dietary strategies that have been employed and studied in the past, one of the oldest strategies, given that energy deficit is required for weight loss, is to feed a very, very low energy diet. And depending upon the low energy diet approach, these could provide significantly less than what most athletes' recommended energy needs for a given day would be. And usually, we look at the example of SlimFast. This is one of the most common very low energy diet approaches. These usually take the form of liquid meals that contain the recommended daily intakes of macro, micronutrients, which is a major concern, and we'll talk about micronutrients a little bit more next week.

But one of the concerns with in taking such low levels of energy is that you will create micronutrient deficiencies because a lot of the foods, or most of the foods, that contain the macronutrients or energy-yielding nutrients also contain important micronutrients. Another concern is that these meals that these liquid meals try to address, rather, is they try to have a relatively large amount of protein in order to try and stave off some of the loss of lean mass or, or muscle wasting, as well as a relatively small amount of carbohydrate, usually less than 100 grams per day, in an effort to further the reliance on fat as a metabolic substrate at rest and during activity.

However, these, while these diets, obviously because of the large energy deficit that they create, um, are effective in rapidly losing weight, the limited availability of carbohydrate, as well as micronutrient deficiencies, and the fact that although these have a typically a relatively high proportion of protein in the calories that make up these, these meal replacement shakes, they still don't have anywhere near enough protein in order to fuel the needs of athletes and exercisers. And so, as a result, a lot of body weight that is lost occurs via the loss of protein and comes at the expense of losing glycogen when you, when you, um, when you ask an active individual or athlete or an exerciser to, to take on a diet that is very low in energy. And of course, given that these types of really restrictive eating practices may lead to decreases in performance, we usually don't recommend these for athletes for those reasons.

A much more maintainable approach that can help avoid both macro and micronutrient deficiencies while maintaining a negative energy balance and weight loss is to restrict energy in a more moderate fashion. And I think the age-old adage here was that if you subtract 500 calories, um, a day, that should equal an energy deficit of 3,500 calories per week, which is roughly equivalent to one pound of body weight. But it's definitely not that simple, and it certainly doesn't account for individual differences in total energy requirements. So, the better recommendation is that once you've figured out, um, the total energy requirement, then to subtract about 20 to 30 percent of that, so that you're creating a small or moderate energy restriction, and negative energy balance will be more sustainable and allow for appropriate intake of both macronutrients and micronutrients to occur that can help maintain performance.

Any discussion of weight maintenance must include a discussion of how the appetite is regulated, or the, um, the drive to eat. And we know that this is primarily controlled in a specific area of the brain known as the hypothalamus, specifically the arcuate nucleus of the hypothalamus. And this area of the brain receives several peripheral neural, metabolic, and endocrine signals that help to regulate appetite in order to adjust energy intake and expenditure in order to achieve a balance. And this happens both in the long term as well as the short term.

And the set of signals that the hypothalamus receives, uh, in response to long-term control of energy expenditure are known as tonic signals. And these generally respond to the metabolic state of fat-free mass and fat mass. So, if we start with fat mass, the primary hormone that helps regulate, or is designed to help regulate, energy intake and expenditure in adipocytes, or body fat, is the hormone leptin. And when fat mass increases, the release of leptin from those adipocytes also increases. And when that leptin binds to the hypothalamus, it's designed to create a tonic inhibition of energy intake. So, the increase in the size of those fat cells is meant to send a message to the brain that, hey, we've got a lot of stored energy around, it's time to reduce our food intake and increase our energy expenditure so that we can achieve an energy balance.

Now, one of the classic problems with this is that it tends not to work very well in overweight or obese individuals who make so much leptin and ignore the leptin signal for a variety of reasons and end up being resistant to this signal. Um, so in situations where large amounts of fat mass are accrued, leptin resistance occurs, and the leptin signal doesn't create as much of a tonic inhibition of energy intake and leads to a positive energy balance and further weight gain.

We also know that increasing muscle mass, as we just discussed, will increase the resting metabolic rate in an effort to, in an effort to get enough energy to maintain that metabolically expensive tissue. And so, this is also sensed in the hypothalamus, and an increased, um, demand and drive to eat is created, uh, when lean mass is, is gained.

Now, we also have to think about short-term control of energy balance, and these are referred to as our episodic signals, or those signals that take place on a meal-to-meal basis. And the majority of our episodic signals are controlled or formed in the gastrointestinal system. And we have one specific hormone that is made in the stomach that is an appetite-stimulating hormone, and that hormone is known as ghrelin. And ghrelin often gets referred to as the hunger hormone because as ghrelin levels, um, increase as a, in a period of restricted food intake, um, or in the absence of a meal, that sends the signal to the hypothalamus to increase energy intake. So, it's an appetite-stimulating hormone.

The other signals that are made in the gastrointestinal system are primarily ones that are made in the, in the small intestine, and these are appetite-inhibitory hormones. And the three most well-studied appetite-inhibitory hormones that are made in the small intestine are cholecystokinin, polypeptide YY, and glucagon-like peptide-1. So, these hormones are released in the small intestine when there is plenty of energy available in the gastrointestinal system and are meant to send the signal to the brain to reduce energy intake.

Now, of course, we have to, if we're talking about weight maintenance and athletes, consider the fact that exercise has effects on both the episodic and the tonic effects on energy balance. And some of that, in terms of the tonic effect, is of course due to the effect of exercise on body composition. However, we also know that exercise can potentially impact the episodic bouts of eating and have an impact on the, have an impact on both appetite-stimulating hormones as well as appetite-inhibitory hormones. So, there are a variety of factors that may potentially lead to either an increase or a decrease in energy intake and energy expenditure as a result of exercise.

In regards to the effects of different macronutrients on what's known as satiety, and so satiety is an episodic effect on energy balance, or an episodic signal, and it refers mainly to the inhibition of eating following a meal. So, when someone feels satiated, they feel satisfied, uh, and they then cease eating. And it can be a reflection of both the interval between meals as well as the amount of food that is consumed when it is offered again.

And when we think about satiety, it's important to understand that not all macronutrients have the same effect on satiety. And if we take a look at the comparisons of different macronutrients on satiety, several studies have shown that foods that are high in protein have a much stronger effect on satiety than high-fat and, or high-carbohydrate foods. And this has been really well studied in terms of what the mechanisms are by which protein induces greater levels of intra and inter-meal satiety. And it absolutely has to do with its effects on the episodic gut-brain axes and hormones that control, um, that control episodic eating.

And the first is that, uh, in comparison to a high-carbohydrate or a high-fat food, a high-protein food will lead to less of an increase in ghrelin when that food is eaten. Um, so with less of an increase in ghrelin, remember ghrelin is the single, um, brain-gut peptide that, uh, that stimulates appetite. So, a decrease in ghrelin would lead to greater satiety following that meal. And then, if we look at the effects on all three of our episodic hormones in the brain-gut axes that inhibit appetite, we see that in all three cases, um, cholecystokinin, glucagon-like peptide, and peptide YY all increase in response to a high-protein feeding in comparison to a high-fat or high-carbohydrate feeding. And because of these, these lower levels of appetite-stimulating hormones and higher levels of appetite-inhibiting hormones, usually a high-protein food will produce an acute decrease in appetite relative to foods that are higher in carbohydrate and fat.

We also need to consider the thermic effect of different nutrients, or how much ingesting a given nutrient increases the metabolic costs of digesting, absorbing, and metabolizing that food. And if we look at the thermic effect of all three macronutrients, we will undoubtedly see that ingesting protein causes the, the highest increase in energy expenditure as a cost of digestion, absorption, and metabolism. So, digesting, absorbing, and metabolizing protein is less, uh, efficient in that it increases energy expenditure by about 20 to 30 percent per unit of ingestion. And if we look at that and carry that over to studies that have looked at the thermic effects of different diet compositions, we can see that in comparison to a high-carbohydrate diet or a more balanced diet, a high-protein diet will, will result in a slightly larger thermic effect, so about 30 or so, 30 calories more will be expended from a high-protein diet than something like a high-carbohydrate or a more balanced diet. So, it just costs more energy to break protein down.

And when we are thinking about why the thermic effect of protein is, is causing these increases in energy expenditure, this is subject to more investigation. However, it is thought that the increased thermic effect for protein is likely due to the energy costs associated with postprandial protein synthesis. And we discussed in our last unit how ingesting or eating protein will cause an increase in the free amino acid pool and cause an increase in protein synthesis, and that that process is energy costing. So, if we also then think about energy storage, because, um, because this process is less efficient, a smaller number of the calories from protein are converted to stored energy in comparison to fat. And that's completely due to the differences in the thermic effect of protein versus carbohydrates or fat.

So, given the satiating effects of high-protein foods, as well as their effect on dietary-induced thermogenesis, um, studies have looked at the effects of a high-protein diet, or a diet that is about 30% protein compared to 10 to 15% in terms of the overall energy content, on, um, on weight loss and weight maintenance. And if we take a look at a study by Weigle et al. that was done in 2005, this, they took 19 healthy subjects. So, these were not overweight or obese subjects, and I think that's important to understand here, that these were, um, these were healthy subjects who all had similar levels of physical activity and were not considerably overweight or obese. And they conducted a controlled feeding study.

And in this study, they started in the first month. They started with a two-week lead-in period in which they fed them enough calories to maintain their weight. So, they weren't inducing any negative energy balance that would lead to weight or fat loss. And that had a pretty standard macronutrient composition of about 15% protein, 35% fat, and 50% carbohydrate.

In the following two weeks, they gave them a diet with the same amount of calories meant to maintain weight, but they gave it to them as a high-protein diet. So, they increased the relative proportion of protein to 30%, decreased the proportion of fat to 20%, and kept the proportion of carbohydrate the same. So, getting them used to the higher protein diet, but not giving them an energy deficit to now deal with on top of that macronutrient manipulation. And then, in the 80 days following that period of time, they kept them on the high-protein diet, and they told them that they could eat as many calories as they wanted as long as they stuck to the controlled feeding. So, they controlled everything that the individuals ate, and they were able to consume as many calories as they want, but the foods that they were consuming led to a macronutrient breakdown of a high-protein diet that was similar to what they had done in the two weeks previous.

So, if we take a look at what happened over the course of this 120-day study, first, we can see that here's the first two weeks where they gave them enough calories to maintain their weight in the form of a more standard macronutrient breakdown with 15% of energy coming from protein. And then they had them come back, and they reassessed their, their overall weight and energy intake. Um, and then after that two-week period, they had them do the same thing again. So, they had the same number of calories meant to maintain weight, but were given, uh, 30% of those calories in the form of protein. And then this would be the 80-day period following where they were able to eat as much as they wanted as long as they stuck within that 30% protein macronutrient breakdown.

And if we take a look at what happens to energy intake, as you would expect, because this is a controlled feeding study, they didn't really change their, they were able to maintain that same level of energy intake regardless of where the macronutrients were coming from. And also, as you would expect, if we take a look at the effects on their body weight, their body weight didn't really change much over the course of this first month, regardless of where the macronutrients were coming from. So, this is a reaffirmation of the fact that energy intake is going to be the primary component of weight loss and weight maintenance, regardless of where those calories are coming from.

But then, if we take a look at what happens when you change that macronutrient content and tell the individuals that they can eat as much as they want, well, the first thing that we have to see here is that when given ad libitum calorie consumption, they, uh, ate significantly less. They consumed significantly less energy, on average about 460 calories less was what was observed in this study. And that they were able to maintain that energy deficit over the course of an 80-day period, which is a, or a 90-day period, rather, which is a really long period of time to maintain that energy deficit. And as you would expect, as a result of that energy deficit, they experienced significant losses in body weight. The average amount of weight lost by participants over the course of the study was around five kilograms. And they also assessed their body composition via DEXA and found that the majority of that weight, about four out of those five kilograms, was made of body fat.

So, by increasing the protein content of the diet, they were able to intake less energy, very likely due to the effects of protein on satiation, and they were able to decrease their body fat, potentially as a combination of both the thermic effect of protein, but also, um, the fact that they were getting larger than normal amounts of amino acids and keeping that free amino acid pool at a level where they could lose less lean mass and lose more fat mass as a result of that energy deficit.

Now, while research has shown us that foods high in protein tend to be the most satiating, they've also shown us that foods that are higher in fat tend to be the least satiating. And so, that's not to say that fat isn't an essential component of the diet. It obviously is. If we take a look at the fact that it represents, um, at least 20% of energy intake, even in the face of increasing protein intake, and that in really low-carbohydrate diets, increasing the energy content that's coming from fat is going to be a requisite, along with increasing the amount from protein, in meeting energy demands. Um, but foods that are higher in fat have been shown to be the least satiating, and the reason for that is because of their high palatability.

Now, what is palatability? Palatability is a subjective measure of a food's pleasantness. So, this is one of the reasons that foods that are higher in fat just taste really good. They have high levels of palatability. Fat adds pleasing texture and taste to food, and so foods that are higher in fat are normally more palatable. And they also are more energy-dense. And we know that because for every gram of fat, there's roughly nine calories of energy. When we look at the volume of food, any volume of food in a high-fat food is going to have significantly more energy in it than a food that is higher in protein or higher in carbohydrate. So, it's got more calories per unit volume and is therefore more dense.

And given that these foods, um, are highly palatable and energy-dense, they lead to lower intra and inter-meal satiety. And we'll take a look at energy density and its effects on satiety in a moment. But because significantly more calories are ingested for a smaller volume of food when the food is high in fat, typically individuals report feeling less satiated during and between meals when they eat high-fat foods. And so, this high palatability and energy density oftentimes can lead to what's known as passive overconsumption, or eating more calories than are needed without actually thinking about it and getting those signals to the brain to inhibit energy intake.

So, when we look at combination foods, right? We can talk about all we want the effects of these nutrients in isolation, but the fact is that they're generally eaten in combination. And because of the satiating effects of protein, as well as the effects on fiber, given that again, fiber is typically not digestible and it adds bulk to most foods, foods that are high in fiber or protein seem to sustain, uh, satiety for longer than those that are high in fat because of the palatability factor here. But also foods that are high in things like white flour or sugar. And the reason that foods that are high in sugars or flours are less satiating has to do with the glycemic index of those foods.

So, if we take a look at something, um, like boiled potatoes, which are mostly carbohydrate but have a lot of fiber in them and a small amount of protein, or something like baked fish, which has a lot of protein and potentially can be baked with whole grains that contain fiber, or oatmeal and milk, that would be really high in fiber and also have a solid amount of protein in it as well. We see that these foods, um, generally produce higher levels of satiety than something like a cake or donuts, a candy bar, or a croissant that are going to be really high in both fats, as well as, as well as high glycemic index carbohydrates. And these high glycemic index foods generally result in a larger insulin response in response to the fact that they're rapidly digested and absorbed and cause significantly higher effects on blood sugar.

And so, when these foods, um, when these foods are eaten, this large insulin response is sensed by the brain in the hypothalamus. Those spikes in blood sugar occur rapidly, and that sugar is then removed from the blood rapidly and causes transiently, uh, steeper decreases in blood glucose and will lead to the desire to eat, lower satiation, and the craving for more foods that contain high amounts of sugars and fats.

Another thing that has been studied that I just mentioned a bit ago was this concept of the energy density of meals, or the caloric value of food per unit of weight or volume. And this has been studied pretty extensively in research. And I want to take a look at one of the classic studies that took place in a group of young women. Again, I think it's important to note here, since we're talking mostly about athletes and exercisers, that this is not an obesity study. These were women who were at, at a healthy weight. And they provided them with meals and snacks for two days, uh, and in a crossover fashion, they had them consume, um, contents of meals that had different energy densities. So, they compared the effects of giving them the same portion sizes with less energy density in these portion sizes, and they looked at the effects of consuming lower energy-dense foods, so those that were of similar portion size but contained less calories, compared to those that were of similar portion size and contained more calories. And they looked at the effects on their overall daily energy intake as a result of these feeding strategies.

And not surprisingly, they found that when individuals ingested lower energy-density foods, when matched for portion size, they consumed significantly less energy per day than they did when they were eating the higher energy-density foods. But perhaps the more relevant finding is that when they were given these lower energy-density meals and snacks, there were no differences in their ratings of hunger or fullness. So, when eating a similar volume of food, and researchers have suggested this might be due to just the visual appeal of foods that are higher in volume with the anticipation that those foods are going to be more filling or more satiating.

But one of the things that it led to investigation of was the analysis of diets in order to determine which types of food intake are more related to lower energy density values. And not surprisingly, individuals who have higher fruit and vegetable intake usually have the lowest dietary energy density values. And that's due to the high water and fiber contents, as well as the low fat content of fruits and vegetables. And to achieve, in helping to achieve this lower energy density diet, so by giving a similar volume of food but having less calories per unit of weight in that food, is a way to manipulate the overall energy intake of the diet in a fashion that may not lead to a significant increase in hunger, um, or fullness as a result of that decrease in energy content.

Another popular strategy for weight loss is that of low-carbohydrate diets. And we discussed low-carbohydrate or ketogenic diets previously, and we saw that they are capable of producing weight loss pretty rapidly in the short term. And that a decent amount of that weight, especially if significant levels of ketosis are induced, might come from a greater reliance on fat as a fuel source. But we also have to remember that in many cases, because of the limits to carbohydrate availability, especially in individuals who are highly active, a lot of the weight loss might be coming from the depletion of glycogen. And the reason for that is because we know that along with each molecule of glycogen that is stored, we also store water along with it. So, when you deplete glycogen, some of the weight loss that occurs is going to be due to the loss of water.

But this is another part of the reason why this works in rapid weight loss, or in situations where cutting weight for something like a weight category sport like wrestling, or mixed martial arts, or weightlifting, might be a desirable short-term strategy. But if we take a look at what happens in the long term, um, a pretty recently published meta-analysis, uh, by Hall and Guo, doesn't support the use of low-carbohydrate diets for long-term body fat loss. So, when you compare these diets to something like energy restriction or moderate energy restriction, after, after a couple of months or after several months on the low-carb diet, that fat loss begins to slow. And diets that rely more on moderate energy restriction will produce similar losses in fat over time, if given sufficient amount of follow-up to actually measure and observe those results.

And these studies have shown that fat loss begins to slow primarily because people have a really hard time sticking to these low-carbohydrate diets. They're extremely restrictive. And I think we can all agree that for an athlete, restricting carbohydrate in the long term and significantly challenging their storage of carbohydrates over the course of a competitive year is probably going to cause some relatively difficult-to-deal-with side effects.

So, if we take a look at this meta-analysis, in which they looked at 32 controlled feeding studies, and so this would be an N of about 562 individuals, with isocaloric substitution of dietary carbohydrate for fat, but everything being equal in terms of protein content, only three out of the 32 studies examined showed a long-term improvement in body fat loss with the low-carbohydrate diet. So, if long-term fat loss is what is desired, then these low-carbohydrate diets probably aren't any more effective than moderate energy restriction in producing those effects.

So, if we take a summary of weight loss strategies for athletes, this is taken from a really recent position stand, 2019, from the International, um, Association of Athletics Federations. Uh, it was published in the Journal of Sport Nutrition and Exercise Metabolism. The first thing that we'll remember is that we know that there are some types of sports where the need to make weight encourages athletes to try to lose weight in relatively short periods of time. And there can be several risks to losing weight in this fashion that are related to the extremely restrictive practices that athletes undergo in order to achieve these rates, primarily dehydration, um, can be one of the main factors that occur, as well as the effects on lean mass, as well as the effects on storage of carbohydrate and availability of carbohydrate as a fuel source. So, these are risks that we have to be aware of.

Now, if athletes are seeking to lose weight and fat more long-term, a more sensible approach would be a moderate energy restriction in the fashion that we previously discussed, so about 20 to 30% below their, um, their total daily energy requirements, with a moderate increase in protein intake, um, in order to ensure that less of that weight comes from lean mass and more of it comes from fat. Um, and again, so the requirements here would be up to a 30% reduction, uh, in total energy intake, and increasing their protein requirements during these times of moderate energy restriction that can go up to as high as 2.5 grams per kilogram per day in athletes who are seeking to achieve high-quality weight loss, or weight loss that is coming more from fat than it is from lean tissue.

Uh, one effective strategy for achieving this is not just to increase the, um, the amount of protein to a moderate level, but also to decrease the energy density of meals by adding fruits and vegetables or things that add bulk and fiber without adding more calories. And this strategy ultimately would be most beneficial because it allows for a reasonable amount of carbohydrate and protein intake, which will allow the athlete to restore their levels of carbohydrate and still perform high-intensity training without major reductions in their lean body mass and associated decrements in their performance.

Now, of course, there's been a considerable amount of work that has gone into studying weight loss, but also there may be situations in which an athlete might want to gain weight. And usually, when it comes to gaining weight for athletes and exercisers, the goal is usually to not to improve fat mass, but rather to improve their lean mass. And this can be a goal of an athlete's nutrition regimen for a number of reasons, but primarily, we can, we can safely assume that one of those reasons might be to improve their strength and power.

We know that by improving the cross-sectional area of their muscles and the protein content of their muscles, that they'll be able to generate more force, more power, and do more work, which is going to be clearly related to performance in a lot of sports. We see the example given here of a rugby player, a sport where strength and power are prerequisites for performing at a high level. Other than that, we may be dealing with athletes who are recovering from some kind of injury where they're trying to rebuild tissue that was damaged and that has potentially atrophied as a result of disuse. So, in these situations, we might be trying to rehabilitate the affected area and muscles that surround that area and provide a stimulus for weight mass accrual so that they can get back to play or training sooner.

And then, of course, there are some situations which may cause an athlete to lose some unwanted mass, like an illness. If they have some sort of stomach virus or some sort of illness where they haven't been able to achieve sufficient levels of energy intake, or that that illness has, has drained them energetically and forced them to not be able, not be able to maintain their lean mass, then we might need to, um, to employ some sort of weight gain strategy as they recover from this particular illness.

Now, unfortunately, as you might imagine, far less work has been done in this area than there has been in with respect to weight loss, but we do have some guidelines that we can go off of in terms of best practices for gaining weight, but also making sure that that weight is the type of weight that the athlete wants to gain.

Now, hopefully, at this point, you've gotten the impression that while energy balance is not the entire picture, it certainly is the most important part of the picture. So, when we think about recommendations for how to gain lean mass, the same thing is true, just the inverse, when we're trying to, uh, gain versus lose mass. And it starts with a moderate positive energy balance. So, 20 to 30% above the individual's total energy requirements is the first place to start when making recommendations on how to gain lean mass.

Now, that sounds easy to do, right? Like eating more is always more fun than eating less. But in, um, and if we think about that part of gaining lean mass is going to be increasing your protein intake, well, we know that protein is more satiating, it inhibits calorie intake when you increase the relative proportion of protein in someone's diet. And we know that the thermic effect of protein is greater. So, we know that these are going to make achieving this positive energy balance more difficult, along with the fact that as an individual gains lean mass, their resting metabolic rate also increases. So, they then need to eat more, um, in order to achieve that relative, um, that relative moderate positive energy balance.

And so, one of the things that you can do to make this easier is to increase the energy density of meals. And so, we talked about this with respect to weight loss and decreasing the energy density of meals by adding things with more, um, vegetables and fruits and fiber and things that are higher volume and lower energy foods. But the opposite practice may be helpful in regards to weight gain. So, this could be a situation where adding a simple source of fat or an energy-dense food may be a good way to increase the overall caloric value of the same volume of food or the same meal, making a positive energy balance easier to achieve.

Again, achieving a higher protein intake, uh, is going to be an absolute prerequisite for gaining lean mass. And we talked about what the recommended rates of intake are for athletes who are in different types of sports last time. And we should also mention that if hypertrophy, or gaining muscle mass, is the goal, then that high protein intake also needs to be met with a program of resistance training. So, so moderate to high load resistance training is going to be required in order for muscles to grow in combination with that high protein intake.

And then let us remind ourselves that if we're trying to optimize protein synthesis and create a positive protein balance through training and through the intake of protein, we have some solid recommendations that have been proven through research to work. And those recommendations are that 20 to 25 grams, or, or a more relative value would be 0.4 grams per kilogram of body weight per meal, um, is ingested, uh, at regular intervals, uh, so every three to four hours, and that that protein contains 8 to 10 grams of the essential aminos and at least 3 grams of leucine, given its potent anabolic effects on the mTOR pathway and protein synthesis.

And then, finally, something we didn't mention in our previous discussion is that ingesting a larger dose of a slow-releasing protein. So, if we think about slower-releasing proteins, and we look at something like casein, which can be found in really high quantities in stuff like Greek yogurt, we know that those proteins don't necessarily give as rapid of a spike in protein synthesis, but they help to maintain protein balance over longer periods of time. So, ingesting something like 0.6 grams per kilogram of body weight per, um, pre-bedtime meal of a slow-releasing protein can help augment overnight muscle protein balance and subsequent muscle adaptations.

So, a really popular dietary approach that has come into light in recent years is this idea of intermittent fasting, um, or periodically abstaining from calorie consumption for, uh, periods of time that would extend beyond what you would do during an overnight fast or a typical bout of sleep. And these diets have taken on many different forms, but they mostly fall into one of three different categories.

And the first intermittent fasting approach is the idea of alternate-day fasting. And during this alternate-day fasting approach, there is, as the name would suggest, an alternation between days in which ad-libitum calories are consumed with days in which only 25% of total energy requirements are consumed. So, going back and forth between days where individuals eat as many calories as they want to versus days where they significantly restrict their energy down to a quarter of what is required, um, for their total daily energy needs.

The second approach to this is a time-restricted feeding approach. And so, this is probably the most, the most popular type of intermittent fasting diet. And rather than going through alternated periods of ad-libitum feeding with significantly low, significant amounts of energy restriction, this involves dividing, um, the day into 16 to 20-hour periods where no calories are consumed, with a four to eight-hour feeding window. So, it's a little more consistent in its day-to-day approach, but it restricts the opportunities to eat into very specific periods of time during the day.

And then the final approach is known as whole-day fasts, or you may see these also called the 5-2 approach. And that approach involves ad-libitum consumption, um, on five to six days out of the week, with one entire day of fasting, or two entire days of fasting out of the seven days of the week. So, all of these approaches, um, as you may imagine, involve periods of time where energy is significantly restricted in terms of what the opportunities that individuals have available to eat to them.

So, these have been a really popular weight loss strategy in recent years. And there are, as you may potentially imagine, some negative fasting adaptations that could occur that might impact performance in athletes. And if we start to think about what those possible negative outcomes might be, first and foremost, during these periods of fasting, especially if they are exercising and they're exercising at times when consuming carbohydrates post-exercise would interfere with their fasting window and not allow them to take advantage of the rapid stage of glycogen re-synthesis, one of the problems with these diets is that it significantly, it can significantly impair muscle glycogen storage.

The same thing would be true too, in terms of liver glycogen restoration, particularly if they need to exercise prior to breaking the fast. Remember that after an overnight fast, liver glycogen levels can drop to below 20 grams. And so, that's one of the reasons that we recommend on the day of performance or competition that carbohydrates are ingested upon awakening in order to restore those liver glycogen levels. So, that can be more challenging, particularly, uh, depending on where exercise occurs relative to the fasting window, or just where the fasting window is taking place in general.

Another issue that is related to some of the things we talked about with the gut is that after abstaining from food intake for longer periods of time, there might be some gastrointestinal issues. If you can imagine, let's take an example of the time-restricted feeding window, where maybe we have a four to eight-hour period in which to get all of our energy and macro and micronutrient needs for the day. In, um, eating that amount of food in a shorter period of time can cause some gastrointestinal issues, some limits to gastric emptying that may occur, specifically if an individual isn't used to doing this.

We also, of course, run the risk of spending large periods of time in a negative protein balance. And this is related to the effects on carbohydrate, and is particularly a concern if consuming protein post-exercise would interfere with the individual's fasting window. We know that there may be a small increase in the reliance on amino acid metabolism during fasting periods. Now, this is somewhat contended, but it has not yet to be disproven that this is true. However, one of the things that we have to consider is that during a period of fasting, we are going to have significantly lower levels of free amino acids in the free amino acid pool, which is going to make achieving protein balance, or a positive protein balance, during those times of the day more difficult.

And then, of course, just by restricting when you can eat, you're going to have limited eating opportunities. So, when this happens, it definitely increases the chances that inadequate energy intake to fuel, um, those energy demands of training that are observed in athletes, is going to be more challenging. And of course, increasing the risk of inadequate energy intake is going to increase the chance that both macro and micronutrients may be present in deficient amounts in the diet.

So, let us briefly consider the alternative here, which is that there might be some potential positive fasting adaptations. Think some of these are parallel to what proponents of low-carbohydrate diets suggest in terms of exercise and positive adaptations. But proponents of this diet suggest that relying more on fats and less on carbohydrates when exercising in the fasted state may spare muscle glycogen during exercise.

Now, I think we also have to consider that in order to do that, we would need to ingest significant amounts of carbohydrate during the feeding window that would allow for glycogen to be replenished. And that limiting the opportunity to eat may affect our ability to do that. And that potentially, as we adapt to exercising in this state, that in a similar fashion to low-carbohydrate diets, that we might be able to rely more on fats at higher intensities of exercise and produce shifts in the maximal rate of fat oxidation to occur at higher percentages of an individual's VO2 max.

Um, and then one of the things that has also been suggested, and this is probably the primary reason why a lot of endurance athletes undergo periods of fasted training, and we've kind of seen this again in relation to glycogen supercompensation and restricting carbohydrate in the diet in order to improve the storage. We know that that glycogen synthesis is more rapidly restored when glycogen levels are low. And so, after exercising in a fasted state, when post-exercise carbohydrate intake occurs, it may result in an improved ability to store glycogen.

The other potential benefits that are touted are that these will reduce body weight and body fat. And again, in a similar fashion to how low-carbohydrate diets suggest that inducing ketosis by limiting carbohydrate availability is going to allow us to rely more on fats as an energy source. And some low levels of ketosis can be induced by a, by an acute period of fasting in 12 to 24 hours, but not to the same degree as if you were to limit carbohydrate intake over the long term.

But I think what is definitely relevant is that a period of fasting is a physiologically stressful state, as well as exercising is a physiological stressful state. And that both actually increase our levels of circulating epinephrine, which stimulates the breakdown of triglycerides into their fatty acids, making them available for energy metabolism. So, that's a possible effect of fasting that may improve, may, um, allow for more body fat to be burned.

But I think regardless of all of that, um, the most significant effect of these diets on body fat is just due to the limited opportunities to eat. When you restrict time feeding windows down to four to eight hours a day, or you have entire days where a quarter of the energy needed to maintain balance is being given, um, or entire days where no energy is being ingested whatsoever, you ultimately end up eating fewer calories by restricting those opportunities to eat. And this potentially could lead to weight loss and does lead to some relatively, uh, rapid weight loss, kind of in the same vein as where, uh, severe energy restriction may, um, occur.

But if you take a look at studies that have compared these diets to, uh, compare these diets to energy restriction or more moderate energy restriction in the long term, they're really no more effective in terms of their effects on weight loss. So, while they may help produce a negative energy balance by limiting the opportunity to eat, if you find other ways to create that negative energy balance through more moderate restriction, then you can achieve the same degree of weight and fat loss long term as you can as you can with one of these intermittent fasting approaches.

Now, if we're going to talk about intermittent fasting as a weight loss strategy, we need to also consider that individuals take on fasts for reasons that aren't related to their weight. Um, and a really good example of this are Muslim athletes during the period of Ramadan, where due to their religious practices, they're not able to intake fluid or foods for significant periods of time. And we can imagine how that might be limiting for performance and training for these athletes. And so, what I want us to think about, and what I want to leave you with, is are there strategies that can be employed that allow athletes who are fasting for non-weight-related reasons to maintain these practices and limit some of the potential negative impacts on their performance?