3 Surprising Things I Learned In My Sports Nutrition Class

You might be surprised, too.

Can you eat too much protein?

This past semester at Oregon Health & Science University I took ‘Sports Nutrition,’ which presented current research findings concerning energy metabolism and the nutritional needs for optimal human performance. These are the topics that I was most interested in and surprised to learn.

Based on the available data, high fat and/or low-carb diets are not recommended for athletes.

Recently, there’s been a lot of coverage in the media regarding the success of low-carbohydrate, high-fat (or even ketogenic) diets among athletes. Lebron James and Dwight Howard are two professional athletes who have been in the spotlight for losing weight and improving performance after giving up carbs.

The reasoning behind such diets is that while our bodies have a limited store of glycogen, they have a much larger amount of energy stored in fat–upwards of 30,000 calories. However, these stores aren’t as readily available for use as fuel as glycogen is; fats must be broken down into fatty acids and then oxidized, which requires many intermediary steps, before it can be put to use as energy.

Research has shown that training enhances fatty acid oxidation: it makes fat more available as fuel, which prompted scientists to wonder whether athletes could be trained either in an unfed state or a very low carbohydrate state to teach their bodies to rely on fats–and the huge amounts of energy they carry–when they work out.

Theoretically, this would prolong exercise, prevent fatigue, and spare glycogen and that “hitting the wall” feeling you might feel in the middle of game four. These studies investigated the effects of acute high fat feeding (right before exercise) and both short- and long-term high fat diets (Burge, Helge 2002, Lambert). While these studies found that higher fat diets did increase fatty acid oxidation, they didn’t result in any changes in performance, time to exhaustion, or glycogen stores. In fact, individuals on long-term high-fat diets actually showed less improvement while training (Helge 1996).

There are also some practical considerations to make here: training your body to burn fats instead of glycogen for energy during a workout is really only helpful in the absence of glycogen, and I don’t know a single ultimate player who goes to tournaments in an unfed state1. There’s also something to be said about the consistency of your diet: if you’re planning on eating carbohydrates before and during your next tournament, you should also do that while you train and practice.

We’re all metabolically different, and it is possible that you operate better with a higher fat diet (as in, higher than the recommendation of about 35% of calories coming from fat–which is still a lot of fat!). But a very high fat diet — above 65% and up to 90%– is not only not helpful, it’s not very tasty: traditional ketogenic diets rely on lots of heavy cream, butter, oils and very small amounts of fruits, vegetables, and protein (and less than about one apple’s amount of carbs per day—and definitely not alcohol). Plus, the process of reaching ketosis or becoming fat-adapted is not fun: in addition to disrupting your training, you’ll likely feel fatigued, nauseated, and slow for up to a month while your body runs out of glycogen.

Takeaway: Diets with at least moderate amounts of carbohydrates are still recommended for optimal athletic performance. I was really happy to have this one confirmed, because I’ve been telling people that extremely low carb diets can impede performance for years. However, I’m sure that as interest for low carb, paleo, and ketogenic diets continue to increase, we’ll see more studies investigating their long-term effects on both health and performance.

Despite what the research says, however, I recommend finding out what macronutrient ratios work best for you, because there is a lot of inter-individual variability and sports nutrition research can only get us so far! If you’re set on a lower carb diet, I would suggest limiting carbs on lighter training days and bumping up your intake before and after practices and tournaments.

Research is sparse, but athletes have higher needs for certain vitamins and minerals.

Vitamin deficiencies are relatively uncommon in the United States, and I suspect that they’re even lower among the ultimate-playing population. But while you might be meeting the Recommended Dietary Allowances (RDA)–the average daily level of intake sufficient to meet the nutrient requirements of nearly all healthy people–your active body may need more than that.

The reasoning behind this is multifactorial: exercise may increase the turnover, metabolism, or loss of a specific nutrient due to biochemical adaptations associated with training, including an increased number of mitochondria per cell, tissue maintenance and repair, and increased needs to metabolize carbohydrates and protein.

Riboflavin (vitamin B2) and niacin (vitamin B3) are two B vitamins that play a role in the production of ATP, which is generated in mitochondria. The generation of ATP from glucose is a long pathway that relies on a number of enzymes and cofactors to function, including riboflavin and niacin. Exercise increases the number of mitochondria per cell, which increases the number of enzymes with their cofactors that are required–so it makes sense that exercise increases riboflavin and niacin needs. Research–albeit from the ’80s–confirms that athletes need more of these vitamins (Belko).

Several studies have looked at riboflavin and niacin intake among athletes (Woolf, Manore). In general, men have adequate intake for these two nutrients, and many who have a high energy diet are actually getting double the RDA. Some women–who have lower energy intakes–have been found to be deficient.

Vitamin B deficiencies have been linked to impaired performance: in one study, men who were deprived of thiamin, riboflavin, and vitamin B6 for 11 weeks showed a 12% decrease in VO2 max, a 7% decrease in onset of blood lactate accumulation (OBLA), a 12% decrease in oxygen consumption at OBLA, a 9% decrease in peak power, and a 7% decrease in mean power (Suboticanec, van der Beek).

Iron is another micronutrient that has higher turnover with more exercise. Iron is lost through sweat and exercise increases the demand for myoglobin and iron-containing respiratory enzymes. If iron is not replaced or it is depleted, athletes are at risk of developing anemia.

However, if you already have good nutritional status–and are meeting the RDAs for these vitamins–supplementation will probably not (unfortunately!) improve your performance. But these findings are still important, because they indicate that your micronutrients are directly related to your calorie needs: if you have increased energy needs because of your training, you also have increased micronutrient needs. In a nutshell, this means that a healthy, nutrient-dense diet is just as important whether you’re eating 2000 calories or 4000–and eating a whole frozen pizza to get those extra calories won’t help you meet those needs.

Takeaway: RDAs are set to meet the needs of the average healthy person—not necessarily someone with a very high training volume. Whenever your training volume increases, make sure your micronutrient intakes increase concurrently. This will likely happen automatically if you’re eating enough calories from quality food sources to sustain your body weight. If you’re substantially restricting calorie intake, however, you are at risk of subclinical deficiency and may not be performing optimally.

There is such a thing as too much protein.

Recommendations for protein needs generally come in two forms: in grams per kilogram of body weight and as a percent of your total calories. For grams per kilogram of body weight, recommendations are based off of the type of exercise. While endurance athletes generally need 1.2-1.4 g/kg body weight (90 to 105 grams for a 165-pound male), resistance athletes need more–about 1.6-1.7 g/kg (120 to 128 for the same guy). As a percent of total calories, protein recommendations generally range from 10-35%.

Sometimes these recommendations can make your protein intake look pretty small. Take a really active, six foot, 170-lb male who does both endurance and resistance exercise (as we do in ultimate). At 1.7 g/kg body weight, he might need 131 grams of protein to promote muscle repair and growth. Let’s say he needs 4000 calories per day: 131 grams of protein would be just 13% of his daily calorie intake, which seems extremely low for someone of his size and activity level. But he’s still meeting the upper end of protein recommendations and should be supplying his body with plenty of amino acids.

There’s really no evidence that eating above 2 grams of protein/kg body weight has any positive effect on training, performance, or body composition (Hoffman). In fact, the studies that measure the exact amount of protein needed to maintain positive nitrogen balance—when your body is building muscles, not breaking it down—usually find that between 1.47-1.65g protein/kg body weight is sufficient. So just because your protein intake seems low, if measured as a percent of daily calories, you’re probably doing just fine if you’re getting between 1.2 and 1.7g/kg.

Increasing your protein intake just to meet a certain macronutrient ratio means that you might be getting way more protein than your body can process. And while it’s unlikely that you’ll develop severe problems like kidney failure, consuming high amounts of protein does impair the liver’s ability to convert nitrogen to urea and can cause intestinal irritation and nausea. Plus, that extra protein could be cutting into your carbohydrate and fat needs, which are just as important as protein.

Takeaway: If you’re an average athlete (meaning not significantly under- or overweight) and you’re paying attention to numbers, aim to take in between 1.2-1.7 g protein/kg body weight as opposed to a certain percentage of your calories. Adding a few more grams of protein than that is probably fine—but huge amounts probably won’t garner any more benefits to performance or body composition. What will help maximize performance is eating quality sources of protein and spreading them out throughout the day: muscle protein synthesis is higher when it’s spread out, as opposed to taken in all at once.

References

Belko AZ, Obarzanek E, Kalkwarf HJ, Rotter MA, Bogusz S, Miller D et al. Effects of exercise on riboflavin requirements. Am J Clin Nutr. 1983;37(4):509-17.

Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med Sci Sports Exerc. 2002; 34(9):1492-8.

Helge JW. Long-term fat diet adaptation effects on performance, training capacity, and fat utilization. Med Sci Sports Exerc. 2002; 34(9):1499-1504.

Helge JW, Richter EA, Klens B. Interaction of training and diet on metabolism and endurance during exercise in man. J Physiol. 1996;492(1):293-306.

Hoffman JR, Ratamess NA, King J, Falvo MJ, Faigenbaum AD. Effect of protein intake on strength, body composition and endocrine changes in strength/power athletes. J Int Soc Sports Nutr. 2006; 3(2):12-18.

Lambert EV, Speechly DP, Dennis SC, Noakes TD. Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high-fat diet. Eur J Appl Physiol. 1994;69:287-293.

Manore MM. Effect of physical activity on thiamine, riboflavin, and vitamin B-6 requirements. Am J Clin Nutr. 2000;72(2):suppl:598S-606S.

Suboticanec K, Stavlkenic A, Schalch W, Buzina R. Effects of pyridoxine and riboflavin supplementation on physical fitness in young adolescents. Int J Vitam Nutr Res. 1990;60:81-88.

van der Beek EJ, van Dokkum W, Wedel M, Schrijiver J, van den Berg H. Thiamin, riboflavin and vitamin B-6: impact of restricted intake on physical performance in man. J Am Coll Nutr. 1994;13:629-640.

Woolf K, Manore MM. Micronutrients important for exercise. In: Spurway N, MacLaren D eds. Advances in exercise series: nutrition and sport. Philadelphia: Elsevier, 2007:117-134.


  1. for argument’s sake, it may be more helpful for marathoners and ultra-marathoners or other endurance athletes who train at low intensity who don’t have access to food during their runs and who actually do reach glycogen depletion. But this isn’t very relevant to us: as ultimate players, we have an abundance of snacks and foods available to us all day. We’re also not low-intensity athletes, and these same studies indicate that even fat-adapted athletes rely on fast-burning sugar during sprints 

  1. Kate Schlag

    Kate is a Registered Dietitian and holds a Masters in Public Health with a concentration in nutrition from the University of California, Berkeley. As an RD, she is looking forward to a career in sports nutrition and nutrition communications. She started playing ultimate with USC’s Hellions of Troy and now plays for San Francisco Polar Bears.

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