Evidence Based Sports Nutrition

In the search for a competitive edge athletes often look to the practices of top athletes, or the latest theory from a popular guru. By chance, this approach will sometimes lead to a true performance improvement. But usually, the fad ultimately proves to make no difference or even hurts performance. An alternate approach is to look at evidence from research studies where ideas were more effectively tested. The evidence based approach will always seem behind the latest trends. It often takes 2 or more years from an idea to make it through the process of research design, testing, analysis, and publication. But in those same 2 years, many of the once hot trends are ultimately abandoned.

The purpose of this guide is to help athletes and coaches develop nutrition and hydration strategies based on quality evidence. Most of the information in this guide comes from the position statements from the American College of Sports Medicine on nutrition and fluid replacement. These statements were published in 2009 and 2007. After spending some time reviewing the literature, these two position statements still represent some of the most comprehensive reviews available on this topic. They provide a good foundation to build a strategy to guide food and drink choices for endurance athletes. Also, incorporated into this guide is the 2010 review article published in Sports Medicine (O’Reilly et. al) on the topic of the effects of glycemic index on performance and metabolism.

To help illustrate how this information translates into practice, an example 150 (70kg) “typical” cyclist is used for calculations. When the recommendations seem to stretch the limits of practicality I offer suggested modified strategies.

Some important things to keep in mind when using this guide:

All recommendations will need to be tailored to your own personal needs.

Nutrition and hydration deficits will cause decreases in performance but excess intake will not improve it.

Stick to familiar nutrition or hydration on race day.

Use training rides to try out new foods and drinks.

When experimenting, don’t be fooled by a particularly good or bad day. Instead, use what works most consistently.

Eat real food. If it looks like something that could be found in the wild it is probably a better choice than the processed wonder food equivalent.

Daily Needs

Carbohydrates, Protein, and Fat:

The endurance athlete should take in 6-10 gm/kg of carbohydrates and 1.2 – 1.7 gm/kg of protein. For a typical 70 kg (150 lb) athlete that would be about 420 – 600 gm of carbs per day and 84 – 119 grams of protein. Fat should make up 25 – 30% of the total calories. (A quick way to convert your own weight in pounds to kilograms subtract 10% then divide by 2, for example 155 lb, 155-15 = 140, 140 / 2 = 70).

For perspective of what these numbers mean, one popular sandwich restaurant chain claims a foot-long oven roasted chicken sandwich with cheese, veggies, and a bag of baked chips would get you 143 grams of carbohydrates, 50 grams of protein, and 39 grams of fat (or 20% of total calories). Notice that eating an equivalent meal 3 times a day would get you to the lower range of carbs, quite a bit over for protein, and a little short on your fat intake.

From a realistic standpoint, tracking every gram you take in probably won’t happen. A simpler method that works out reasonably well is a 50/25/25 approach. When you sit down to eat, fill half of your plate with vegetables and fruits, a quarter with a lean protein, and the other quarter with a complex carb such as whole grain pasta or a baked potato. The extra carbs you need will come from intake during and around workouts. Rounding out this diet with “healthy” fats by cooking with olive oil, snacking on nuts, or having a fatty fish as your protein choice etc. should get you fairly close to the recommended intake.

Once every couple of weeks or so you can spot check your diet on a typical day to make sure your balance of foods is appropriate. Comparing your actual intake to the general recommendations should give you a sense of any major deficiencies.

Vitamins or supplements shouldn’t be necessary unless you have diet restrictions or are actively trying to lose weight.

Periodically, the cycling press has made the high fat or low carbohydrate diets a hot topic. The concept is that you can train your body to burn more fats during exercise resulting in better endurance by sparing carbohydrate (glycogen) stores. There are some studies that support this idea. However, such an approach carriers a fair amount of risk because of how important carbohydrates are as a fuel source in the typical diet.

Pre-Race Nutrition

Ideally, a high carbohydrate meal should be eaten 3-4 hours prior to the event. Eating 200 – 300 grams prior to events has been shown to improve performance in some studies, and 3 to 4 hours is usually enough time for the stomach to empty. To get this amount of carbohydrate for 9 am start an athlete would need to eat the equivalent of 4-5 bagels at 5 in the morning. Such a large meal might be a bit tough all on its own let alone so early in the morning.

The practical approach is to simply eat a reasonable amount of carbohydrates as early you can. Adjust the size of the meal based on how much time you have before the race to avoid an upset stomach. If you need to eat close to start of the race it may also be a good idea to avoid foods high in fiber, fat, and protein. Foods high in these nutrients will slow down the rate that your stomach can empty leaving you uncomfortable during fast starts.

When choosing pre-race carbohydrates many experts tout the benefit of complex carbohydrates, or low glycemic index carbs. (For simplicity complex carbohydrates are generally starchy foods, while low glycemic index carbohydrates can be starchy foods or foods that contain protein or fat which lower the glycemic index). The complex/low glycemic carbohydrate strategy appears to effective if the only carbohydrate intake will be the pre-race meal. Taking in sufficient carbohydrates during the ride eliminates the performance advantage of the complex/low glycemic carbohydrates. O’Reilly et al make the point that the type of carbohydrate doesn’t really matter as long as you can optimize the amount of carbohydrate before and during your event.

However, I do still recommend complex carbohydrates and low glycemic index foods whenever possible because they tend to be in more nutritious foods. Also, in the real-world setting carbohydrate intake is often not maximized during sports. This reality leaves open the possibility to gain some performance benefit of complex and low glycemic index pre-race carbohydrates.

Notes:

It is ok to eat right up until the start of the event as long as your stomach can tolerate it. Studies looking at the effect of eating within an hour of an event do not show any decrease in performance. This evidence goes against the popular teaching that eating within the hour or two before an event should be avoided.

Pre-Race Hydration

Drink 5 – 7 ml/kg of water (a little less than a 24 oz water bottle) 4 hours before the event. At two hours before the event if you are not urinating clear or very light yellow (dark yellow urine can be a sign of dehydration) drink another bottle. Drinking this amount should correct any minor dehydration. If you are significantly dehydrated, more water will not necessarily help as the ┬ábody can not correct deficits much faster. It is important to drink far enough in advance of the event to give your body plenty of time urinate out excess water. Avoid drinking plain water in the hour before the event as you are likely to find yourself with a full bladder just as you roll off from the start line.

Drinking fluids with salt or protein can help your body hold on to more fluid than drinking water alone. Logic would imply that this may be an effective strategy for events where drinking is difficult or for particularly hot humid days. However, hyper-hydrating has not been shown to improve performance. Attempting to hyper-hydrate with glycerol is specifically not recommended.

Although there may be no performance advantage, a sports drink is likely a better option than plain water in the hour before the start to reduce the chance of needing to urinate at the start of the race. After the race is underway the rate of urine production slows significantly making the need to urinate less of an issue.

Race Nutrition

Carbohydrates

Take in 30-60 grams (1-1.5 bananas, 1-2 gels, or 1-2 bottles of sports drink) of carbohydrate every hour during events that are greater than 1 hour. This amount represents the upper end of what most athletes can absorb during exercise. Carbohydrates that are not absorbed can lead to abdominal discomfort and diarrhea. Experiment during training to figure out how much carbohydrates intake you can tolerate during exercises. When possible choose real foods over processed options

It is important to realize that your body can not absorb enough carbohydrate to keep up with the demand of moderate to intense exercise. Your intake of carbohydrates simply extends the time you have before you run out.

For sports drinks, concentrations of greater than 8% for drinks will empty slower from your stomach. If you stick with the mixing instructions, or using just enough to add some flavor, you will be fine.

Many sports drinks make the claim that maltodextrin, an other polymers, are complex carbohydrates. And as a complex carbohydrate, they have an advantage in increasing your ability to take in large quantity without slowing down stomach emptying or faster absorption. These claims are somewhat misleading as maltodextrin is an chain of glucose molecules connected end to end, i.e. a chain of simple sugars. This chain is broken easily by digestive enzymes and the process starts as soon as it hits your mouth. (Maltodextrin actually has a higher glycemic index than table sugar.)

The type of complex carbohydrate that will not get broken down as quickly have multiple branches rather than a chain. These types of carbohydrates will not taste sweet and are found in typically in starchy foods.

The type of carbohydrate/sugar doesn’t seem to matter from a performance standpoint as long as it is not just all fructose. Fructose by itself is not taken up as fast as glucose or glucose fructose combinations. I have not come across any sports products that contain straight fructose. High-fructose corn syrup, which is found in soft drinks and some less expensive sports drinks, probably isn’t as bad as its current reputation as the cause of the obesity epidemic. It is actually fairly equivalent in fructose and glucose balance to sucrose (cane and beat sugar), and honey. Rice syrup contains some complex carbohydrates in addition to simple sugars.

The advantages to different carbohydrates/sugars is mostly the sweetness/flavor and cost.

Protein

Protein intake does not immediately improve performance unless your intake of carbohydrates is suboptimal. The original studies that showed improved performance of 4:1 carbohydrate to protein compared a suboptimal intake of carbohydrates to carbohydrates plus protein. Followup studies that made the total calorie intake the same did not show a performance advantage. However, there may still be a theoretical advantage to taking in protein during exercise as it may spare muscle breakdown and promote muscle growth after exercise. The theoretical discussion is beyond the scope of this guide.

Fats

Fats represent the largest fuel reserve in your body. It is not necessary to take in additional fat during exercise. At low intensity the majority of your energy can come from burning fat. However the rate at which you can burn fat is limited and dependent on carbohydrates. As intensity increases your body is forced to burn a higher percentage of carbohydrate. When your body runs out of carbohydrates you not only lose your ability to sustain high intensity exercise but you also lose your ability to efficiently burn fats making even low-moderate levels difficult to sustain.

Strategies to improve fat utilization, i.e. spare carbohydrates, may provide a performance advantage. These strategies include improving aerobic fitness, intelligent pacing, and diet manipulation. Improving fitness and good pacing are logical and easy to endorse. Diet manipulation however, is difficult to recommend because of the significant potential to cause more harm than good.

Electrolytes

Electrolytes (salts) have not been shown to improve performance. Typical western diets contain plenty of electrolytes to replace anything lost during exercise.

The advantages of salt containing sports drinks are for taste, and to lessen the risk of hyponatremia. Taste is self explanatory. Hyponatremia, or low salt concentration, usually occurs in less experienced endurance athletes who drink too much plain water during an event. As exercise slows kidney function, the body loses its ability to get rid of excess water. In this state an athlete can potentially drink enough water to cause a low salt level caused by dilution. Theoretically, salt containing sports drinks decrease this risk.

Conventional wisdom is that the loss of salt and fluids causes cramping. However, replacing fluids and salts has not been shown to prevent cramping. It has been shown that improving fitness and acclimatization to hot environments reduce cramping AND excessive salty sweating. An alternate explanation may be that both cramping and excessive salty sweating are caused by over-reaching or suboptimal fitness/acclimatization.

Water

Studies show that dehydration (losing 2% of your body-weight) leads to decrease aerobic performance. Aerobic performance continues to fall off as dehydration worsens. Anaerobic performance is less affected by dehydration.Water intake should roughly match your rate of water loss through sweat and evaporation. For endurance athletes this can range anywhere from 0.5 – 2 L per hour depending on temperature, intensity, and individual physiology.

For the hypothetical 155 lb (70kg) rider, a loss of about 1.4kg (about 3 lbs) or 1.4 liters would equal 2% dehydration. Saving a little margin of error it is probably a good idea for the average rider to not to lose more than 1 liter (a little more than a 24 oz water-bottle).

On hot days a good strategy might be to assume a high sweat rate of 1.5 – 2 liters per hour and try to drink enough to avoid losing more than 1 liter. Thinking about hydration in these terms, replacement fluids need to be progressive as the length of the ride increases. For example you might lose:

.75 – 1 L in 30 min

1.5 – 2 L in 1 hr

3 – 4 L in 2 hr

4.5 – 6 L in 3hr

Assuming you have about 1 liter to lose comfortably without affecting performance your minimum intake to prevent dehydration would need to be:

0 L (0 bottles) for 30 min

.5 – 1 L (1 bottle) for 1 hr

2 – 3 L (3 bottles) for 2 hr

3.5 – 5 L (6 bottles*) for 3 hr

*Notice that the 3 hr estimate of 6 bottles is a very large amount of water. Less experienced athletes should gain experience optimizing their hydration with exercise bouts in the 2 hour range to decrease the risk of hyponatremia and dehydration.

The calculations above are likely to overestimate water intake needs for longer events and for well conditioned, properly acclimatized athletes. Also, rate of sweating tends to fall off with time and as the body becomes dehydrated.

Ultimately, trial and error is needed to figure out what your body will need during any given circumstances. Spot checking yourself with pre and post-ride weights can tell you if you are drinking enough, see below.

Recovery

Carbohydrate

Carbohydrate intake should be your priority following hard rides. Within the first 30 min take in 1 – 1.5 grams/kg, about 100 grams for an average rider. Take in another 100 grams every 2 hours for the next 4 – 6 hours or until you have a main meal.

There appears to be mixed data for the best type of carbohydrate to eat after exercise. Without a clear answer my default recommendation is again complex carbohydrates and low glycemic index carbohydrates.

Protein

Protein intake is also a good idea, especially if you are trying to gain muscle mass or have difficulty maintaining it. Studies do show that taking in protein after exercise may promote muscle repair and growth. For endurance athletes the ideal post-exercise intake is not entirely clear. But given that the daily intake is about 1:5 protein to carbohydrate you can probably use this a starting point for recovery intake as well, i.e. about 20 grams of protein in the first 30 min followed by 20 grams every 2 hours until your main meal assuming you are taking in 100 grams of carbohydrates.

Electrolytes

The typical western diet contains enough salt to replace losses during exercise.

Water

The water replacement recommendation is to drink 1 – 1.5 L for every kilogram (16-24 oz for every pound) of body weight lost during your event.

Going on the assumption that most people will not bring scale with them to events calculating your water needs is not entirely practical. Instead, start with the post-race hydration of drinking a bottle of water immediately after the event. Drink another bottle of water every 2 hours until your urine is consistently clear or very light yellow. To check your fluid status compare your pre and post exercise weights. Every 2 pounds of weight loss equals about 1 liter or water deficit (or a little more than 1 bottle).

Recovery Drinks

If real food is not available, recovery drinks are reasonable way to make sure that you get some carbohydrate and protein in immediately after an event. Just check the label to make sure that there is a reasonable ratio of protein and carbohydrate. For endurance sports err on the side of more carbohydrates as their is strong evidence for the benefits of carbohydrates for recovery while the benefit of protein is still theoretical at this time.

References

American Dietetic Association; Dietitians of Canada; American College of Sports Medicine, Rodriguez NR, Di Marco NM, Langley S. American College of Sports Medicine position stand. Nutrition and athletic performance. Med Sci Sports Exerc. 2009 Mar;41(3):709-31.

American College of Sports Medicine, Sawka MN, Burke LM, Eichner ER, Maughan RJ, Montain SJ, Stachenfeld NS. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007 Feb;39(2):377-90.

O’Reilly J, Wong SH, Chen Y. Glycaemic index, glycaemic load and exercise performance. Sports Med. 2010;40(1):27-39. Med Sci Sports Exerc. 2009 Mar;41(3):709-31.

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