Carbohydrate Unloading
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Carbohydrate Unloading |
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A high carbohydrate diet makes you fat, sick, and hurts athletic performance.
Sounds hard to believe? It is.
Yet, that's the premise of several carbohydrate-bashing diet books currently on the market. These books (Enter the Zone, Protein Power, and Healthy for Life) all feature diets that supposedly hold the key to a lifetime of thinness. Their shared theme is that Americans should be eating a high-protein diet, instead of the high-carbohydrate diet recommended by most health professionals. Some of the books even claim that a high-protein, low-carbohydrate diet can prevent and treat heart disease, cancer, diabetes, and depression. In the process, you can also reach a near-euphoric state of peak physical and mental performance.
Do these books provide a better way to eat?
No.
Carbohydrate-bashing diet books claim that carbohydrates are bad because they raise your blood sugar level and cause the release of the hormone insulin -- a supposed monster hormone. According to these books, insulin makes it hard for you to stay, or become, thin. Basically, insulin is treated as the hormone that makes you fat. Insulin supposedly does this by taking your high-carbohydrate food and storing it as fat rather than allowing the body to use it for energy.
Reality check number 1: Carbohydrates and insulin don't make you fat.
Insulin isn't a "monster" hormone -- it's essential for the transfer of glucose from the bloodstream to the body's cells, where it's used to fuel all activities. When it comes to losing weight, what matters isn't carbohydrates and insulin, but calories. Your weight depends on how many calories you take in compared to how many you burn off. Eating a high percentage of calories from carbohydrate doesn't make you fat -- you must eat too many calories relative to your needs for insulin to lay down fat (1).
Paying attention to calories is critical for weight control. When people are encouraged to eat more carbohydrate and less fat, some folks get the wrong message. They think they can eat as much high-carbohydrate food as desired, as long as the food is fat-free. The result -- these individuals can't lose weight because they eat too many calories in the form of low-fat sweets and extra large portions of starches. As a result, they may feel that carbohydrates have "betrayed" them in their quest for weight loss.
The bottom line -- people can't eat an unlimited amount of carbohydrate by cutting down on their fat intake. Cutting back on dietary fat does reduce total calories more than cutting back on dietary carbohydrate, because fat supplies more than twice the calories by weight. Fat is also more likely to be stored as body fat than is carbohydrate. However, a person who cuts back on fat calories but adds them back in the form of carbohydrate calories is not going to lose weight. It's a simple matter of energy balance that holds true for people whether they're active or a sedentary (1).
A high-carbohydrate diet may cause problems for individuals who have insulin resistance -- which is estimated to affect 10 to 25 percent of all Americans. The muscle, liver, and fat cells of insulin-resistant people are less sensitive to the actions of insulin -- most likely due to a reduced number of insulin receptors. The pancreas compensates by increasing insulin secretion to maintain normal blood glucose levels.
Insulin-resistant people who oversecrete insulin are likely to have high blood pressure, high blood triglycerides, and a low level of HDL (high density lipoprotein cholesterol). All of these factors increase the risk of developing coronary heart disease. Carbohydrate-bashing books claim that this oversecretion of insulin causes carbohydrate to be stored as fat. Although high blood insulin levels do raise the risk of heart disease, there is no good evidence that they make people fat. As noted above, it's the total caloric intake that's important, whether a person is insulin-resistant or not (2).
Reducing excess weight and increasing physical activity are more important in the treatment of insulin-resistance than the dietary percentage of carbohydrate or fat. Exercise and weight loss reduce triglycerides, increase HDL cholesterol, and lower blood pressure -- which collectively lower the risk of heart disease. In addition, both weight loss and exercise independently increase insulin sensitivity, which results in lower blood insulin levels (2).
Weight loss allows the cells to more easily "recognize" insulin so that less insulin is required. Regular physical activity is important because muscle cells are the biggest users of insulin. Decreasing the muscle's insulin requirements through exercise cuts down on insulin resistance to a large extent. This means that insulin can bind more easily to the cell receptors and be more effective in promoting glucose uptake (2).
Several of the carbohydrate-bashing books also claim that insulin hurts your health by causing the body to make "bad" eicosanoids. Eicosanoids are hormones that help to regulate inflammation, the blood's tendency to clot, and the immune system. According to these books, "bad" eicosanoids cause most major health problems, such as heart disease, cancer, diabetes, and even depression. "Bad" eicosanoids also supposedly harm performance by reducing oxygen transfer to cells, lowering blood glucose levels, and interfering with body fat utilization.
Reality check number 2 -- eicosanoids don't cause disease or impair athletic performance.
The claim that eicosanoids are all-powerful is ridiculous -- the body's physiology just isn't that simple. There's also no evidence that insulin even makes "bad" eicosanoids (1). By claiming that a high protein, low carbohydrate diet halts the production of "bad" eicosanoids, the carbohydrate-bashing diet books are capitalizing on an unfounded idea. Such health claims are particularly insidious because they create false hope for desperate people who seek a cure for life-threatening illnesses such as heart disease, cancer, and diabetes.
Even though carbohydrate and insulin are not villains, Enter the Zone, Protein Power, and Healthy for Life all recommend complicated, carbohydrate-restricted diets. Supposedly, these high protein, low carbohydrate diets will make you thinner, healthier, and a better athlete. What they really do is take the fun out of eating. Almost all professional health groups in the country recommend 55 to 60% calories as carbohydrate, 10-15% as protein, and the remainder as fat. And not every time you sit down to eat (1).
Reality check number 3: There's nothing magical about these high protein, low carbohydrate regimens -- they're just very low-calorie diets.
You'll lose weight on these diets because of the severe caloric restriction -- not because of what is supposedly happening to your insulin levels or eicosanoids. You'll lose something else, too, eventually. Your performance and well-being. You can't train or compete well for very long on a low-calorie, low-carbohydrate diet. You need to eat enough calories and carbohydrate to maintain your muscle glycogen stores -- the favored fuel for exercise. Following a low-calorie, low-carbohydrate diet will only put you into a twilight zone of near starvation.
Reality check number 4: you need carbohydrates to perform at your best.
Although carbohydrate feedings 30-45 minutes before exercise do raise insulin levels and lower blood glucose, these effects are temporary and will not harm performance. This insulin response does not impair fat utilization or cause accelerated glycogen depletion (3). During aerobic exercise, the rise in the hormones epinephrine, norepinephrine, and growth hormone inhibit the release of insulin from the pancreas. This hormonal milieu enhances liver glucose output and promotes greater fat utilization (4).
In fact, consuming carbohydrate an hour before exercise can improve your performance (5). Carbohydrate feedings three to four hours before exercise also enhance performance by "topping off" your glycogen stores (6). Consuming carbohydrate during workouts lasting longer than an hour aids endurance by providing glucose for your muscles to use when they're running low on glycogen (7,8). And, taking in carbohydrate right after several hours of hard training increases muscle glycogen storage following exercise (9).
As a group, athletes are unlikely to be insulin-resistant because they're lean and they exercise. Furthermore, active people and athletes require dietary carbohydrate to maintain their muscle glycogen stores -- the predominant fuel for most sports. The only way they will gain weight is if they consume more calories than they expend. When this happens, they should blame their forks, not the carbohydrate.
Reality check number 5: High-protein, low-carbohydrate diets don't increase your ability to burn fat.
No diet won't help you gain better access to your body's fat stores so that you'll burn more fat during exercise. Carbohydrate, not fat, is the primary fuel for exercise at or above 70% of aerobic capacity -- the intensity at which most people train and compete (4).
People don't usually work out long enough to burn significant amounts of fat during exercise. It takes about 20 minutes of exercise for fat burning to kick in. Rather, it's the caloric deficit resulting from the exercise session that helps promote body fat loss. A gradual loss of body fat comes from burning more calories during exercise than you take in at the table. Since aerobic training already creates a metabolic milieu favorable for fat metabolism, the best way to crank up your body's fat-burning ability is to keep working out (10).
The bottom line -- you don't need to eat a high-protein, low carbohydrate diet for weight loss, optimum performance, or health.
References
1. Entering a high protein twilight zone. Tufts University Diet & Nutrition Letter. 1996;14(3):4-6.
2. Is pasta now on the "out" list too? Tufts University Diet & Nutrition Letter. 1995;1995;13(3)4-6.
3. Hargreaves M, Costill DL, Fink WJ, King DS, Fielding RA. Effects of pre-exercise carbohydrate feedings on endurance cycling performance. Med. Sci. Sports Exerc. 1987; 19:33-36.
4. Gollnick PD. Energy metabolism and prolonged exercise. In Lamb DR, Murray R (eds) Perspectives in Exercise Science and Sports Medicine Volume 1: Prolonged Exercise, pp 1-36, Indianapolis, Benchmark Press, 1989.
5. Sherman WM, Peden MC, Wright DA. Carbohydrate feedings 1 hr before exercise improves cycling performance. Am. J. Clin. Nutr. 1991; 54:866-870.
6. Sherman WM, Brodowicz G, Wright DA, Allen WK, Simonsen J, Dernbach A. Effects of 4 hr preexercise carbohydrate feedings on cycling performance. Med. Sci. Sports Exerc. 1989; 12:598-604.
7. Coyle EF, Hagberg JM, Hurley BF, Martin WH, Ehsani AA, Holloszy JO. Carbohydrate feeding during prolonged strenuous exercise can delay fatigue. J Appl Physiol. 1983;55:230-235.
8. Coyle, EF, Coggan AR, Hemmert WK, Ivy JL. Muscle glycogen utilization during prolonged strenuous exercise when fed carbohydrate. J. Appl. Physiol. 1986 61:165-172.
9. Ivy JL, Katz AL, Cutler CL, Sherman WM, Coyle EF. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J. Appl. Physiol. 1988; 6:1480-1485.
10. Coyle, EF. Fat metabolism during exercise. Sports Sci. Exch. 1995;8(6):1-6.
Ellen Coleman,
RD, MA, MPH
ellen@cruciblefitness.com
