Is there any benefit to deliberately training with low energy stores?
One of the hottest controversies in current sports nutrition was sparked by an unusual Danish study published in 2005. Volunteers performed a 10-week training program in which they exercised one leg every day and exercised the other leg twice as much every second day. That meant that the leg trained every other day did half of its workouts in a highly fatigued state, having been depleted of glycogen by the first half of the workout. By the end of the study, this leg had developed significantly greater endurance, giving rise to a new concept that was soon dubbed “train low, compete high,” in which athletes seek to do part of their training when their energy stores are greatly depleted (“training low”) so that they’ll perform even better when they’re fully fueled (“competing high”).
There’s no doubt that having full carbohydrate stores improves your endurance. In fact, that’s the point: “training low” is the nutritional equivalent of wearing a weighted vest to make your workout harder. There have long been rumors that athletes like Miguel Indurain, the five-time Tour de France champion, tried this approach by doing some of his training in a fasted state. But there’s been little evidence that it actually works: even the Danish study had several flaws—notably that the subjects were untrained, which makes it much easier to observe improvements in performance, and that “single-leg kicking” isn’t an activity that has any particular relevance to the real world.
Several recent studies have tried similar protocols with trained cyclists, and they’ve found that training low really does stimulate the body to adapt differently—but it doesn’t seem to produce any actual performance benefits. For example, a 2010 study at the University of Birmingham used highly invasive muscle biopsies and isotope tracers to measure the different muscular and metabolic changes produced by training high and training low. As expected, they found that training low taught the body to burn more fat instead of carbohydrate, which should theoretically improve endurance performance by allowing carbohydrate stores to last longer before running out. But in a one-hour time trial, there was no difference between the two groups.
This apparent contradiction is similar to discussions of the “fat-burning zone” for weight loss. In both cases, researchers have figured out how to make the body rely more on fat instead of carbohydrate—but you don’t lose more weight or bike faster, because the body seems to compensate for the change. In fact, there’s some evidence that in increasing your fat-burning abilities, you also harm your carbohydrate-burning capacity. It’s tempting to believe that this doesn’t matter in ultra-endurance events like marathons or 100-mile bike races, where fat-burning plays a major role. “However,” Australian Institute of Sport nutritionist Louise Burke pointed out in a 2007 commentary, “the strategic activities that occur in such sports—the breakaway, the surge during an uphill stage, or the sprint to the finish line—are all dependent on an athlete’s ability to work at high intensities that are carbohydrate-dependent.”
In practice, there are two approaches to training in a carbohydrate-depleted state. One is the approach used in the studies described above: deplete your muscle glycogen stores with 30 to 60 minutes of moderate exercise at about 70 percent of maximum effort. Then, without refueling, do some harder training. Alternatively, you can try working out first thing in the morning without eating anything first, possibly having eaten a low-carbohydrate dinner the night before, so that your whole body is low on glycogen. Both these strategies can be very stressful for the body and shouldn’t be attempted more than once or twice a week. Recovery afterwards is crucial, including lots of carbohydrates.
At this stage, although “train low, compete high” has become a popular buzz-phrase, the research remains highly uncertain. For most people, the best bet is to let others do the risky and often unpleasant experimentation—then, if it does turn out to provide measurable performance benefits, give it a try once the details have been worked out.
Can I get the nutrients I need for a heavy exercise regimen from a vegetarian or vegan diet?
Running 167.7 miles in a single day, as 36-year-old Scott Jurek did in setting a new American record for the 24-hour run in 2010, is a staggering feat by any definition. But Jurek’s accomplishment garnered extra attention because he follows a strict vegan diet. How was it possible, people wondered, to run over 140 miles week after week and consume 5,000 to 8,000 calories a day, with no meat or animal products?
For decades, would-be vegetarian athletes have been warned about the shortcomings in their diets, like the possible shortage of essential elements such as protein, iron, and calories. But only a few isolated studies have compared the actual performance of vegetarian and omnivorous athletes, with generally favorable results. One in 1970 found no difference in lung function and thigh muscle size between the two groups. A 1986 Israeli study found no difference in serum protein between vegetarian female athletes and matched controls, and a 1989 German study found no difference between vegetarians and non-vegetarians in the finishing time of a 1,000-kilometer run.
Spinach (3 cups, cooked): 15 g of protein
Asparagus (3 cups, cooked): 12 g
Lentils (1 cup, cooked): 18 g
Oats (½ cup, dry): 13 g
Quinoa (1 cup, cooked): 8 g
It is, of course, entirely possible to consume an unhealthy and deficient vegetarian diet. If you took a typical North American diet and simply removed the meat from it, you’d almost certainly not get enough protein to support a heavy exercise regimen. But if you take the time to consume good sources of vegetable protein, you’ll have little trouble meeting your protein needs. Similarly, getting enough calories is simply a matter of eating more. “The first thing to worry about isn’t so much what you eat, but how much you eat,” Jurek explained to a New York Times reporter. “You have to take the time to sit at the table and make sure your calorie count is high enough.”
There are, however, some special considerations that vegetarians and vegans need to be aware of. Though leafy greens like spinach and kale are excellent sources of iron, only about 10 percent of iron from plant sources can actually be absorbed by the body (compared to 18 percent from meat). Female endurance athletes, in particular, are prone to low iron levels, so they may need to consider iron supplements if tests show their levels are low. In addition, a 2010 review in the journal Current Sports Medicine Reports by Joel Fuhrman and Deana Ferreri identified several other micronutrients that vegan and vegetarian athletes may be deficient in. In particular, zinc, vitamin B12, and the omega-3 fatty acid DHA are all crucial for physical performance and are either hard to absorb or hard to get enough of from plant sources, so they recommend taking supplements.
“Clearly,” Fuhrman and Ferreri conclude, “a properly designed vegan (or near-vegan) diet can meet the nutritional demands of a speed and agility athlete, such as tennis, skiing, basketball, track, and soccer, but may not be ideal to maximize growth over 300 lb as a football linebacker.” Scott Jurek might disagree with this conclusion, since he manages to consume up to 8,000 calories a day—but there’s no doubt that such extreme consumption requires a special and perhaps rare dedication. Most of us, though, have no desire to exceed 300 pounds or run for 24 hours at a time, so a well-balanced vegan or vegetarian diet is perfectly capable of meeting our needs.
CHEAT SHEET: NUTRITION AND HYDRATION
• To carbo-load, you can max out your carbohydrate stores with just one day of eating 10 grams of carbohydrate per kilogram of body weight.
• To avoid stomach problems during exercise, avoid high-fiber and high-fat foods in pre-exercise meals and allow at least three hours for digestion.
• Eat as soon as possible after exercise (within at most two hours) to enhance recovery and training gains, aiming for a roughly 4:1 ratio of carbohydrate to protein.
• Losing more than 2 percent of your body weight in fluid is thought to hurt performance, but some scientists now believe that simply drinking when you’re thirsty is sufficient.
• Drinking too much can lead to dangerously low sodium levels (hyponatremia) and possibly death. Don’t drink more than eight ounces every 20 minutes.
• For events lasting longer than an hour or two, consume fluids containing no more than 6 percent carbohydrate and some electrolytes.
• Antioxidants like vitamins C and E may block some of the health effects of exercise and slow post-exercise muscle recovery, though the evidence is still preliminary.
• Probiotics can help ward off respiratory infections and digestive problems, but it’s not yet clear which strains of bacteria are best and how much is required.
• Vitamin D (the sunshine vitamin) is crucial for good health and many people require supplementation, but there’s no evidence that extra vitamin D improves athletic performance if you’re not deficient.
• Training with depleted carbohydrate stores (e.g., before breakfast) can teach your body to burn more fat and store more carbohydrates, but there’s little evidence so far that it boosts performance.
• Studies have found no difference in physiology or results in athletes with vegetarian and non-vegetarian diets, provided that the diets are balanced and include all necessary nutrients.