Some people use exercise as a way to control their weight. Exercise does help with weight control, but working out, especially at a high intensity, and aggressive calorie restriction doesn’t mix. Exercise puts great demands on the body. That’s why it’s important to stay well fueled with a nutrient-rich diet. If you cut back too much on calories, you won’t be able to get the most out of a workout. Here are some other problems you can encounter if you exercise without adequate calories and nutrition.
Reduced Exercise Performance and Fatigue
When you do high-intensity workouts, you activate fast-twitch muscle fibers that use carbohydrates as fuel. If you work out with glycogen stores that are depleted due to inadequate carbs, you’ll have more difficulty exercising at a high intensity and will experience fatigue. Your body adapts to a low-carb diet to some degree by becoming more efficient at using fat for fuel, but it takes several weeks for this to happen. In addition, if you do endurance workouts of 90 minutes or more, your body may break down protein from muscle to use as fuel when you’re undernourished. Most people want to hang on to their lean body mass.
Decreased Immunity
Not feeding your body enough calories when you work out takes its toll on your immune system too. Exercising in a calorie-deprived state, especially for long periods of time, increases the release of the stress hormone cortisol. Too much cortisol not only makes it harder to control belly fat, but it also suppresses immunity. You also see this a lot in athletes who overtrain without giving their bodies adequate time to recover. A suppressed immune system increases the risk of catching colds and flu and even developing cancer since your immune system is important for keeping cancer cells in check.
Hormonal Issues
Women who exercise and overly restrict calories may develop amenorrhea and stop menstruating. Exercise and calorie restriction puts stress on the body. This causes the portion of the brain called the hypothalamus to stop signaling the ovaries to produce estrogen, and periods become irregular or stop. This can also happen when a woman’s body fat percentage drops below about 15%. Fortunately, this isn’t permanent. Women can reverse this by increasing their calorie intake, cutting back on their exercise, or gaining weight.
Osteoporosis
High-impact exercise stimulates bone growth and helps to protect against age-related bone loss, but women who stop menstruating from inadequate nutrition and overtraining are at high risk for bone loss. This is because their estrogen levels drop, and estrogen helps to maintain bone density. In women who aren’t getting enough calcium and vitamin D, the problem is magnified. The late teen years and early adulthood are when bone density peaks, and restricting calories too much during this time may lead to bone problems later in life.
Iron Deficiency Anemia
Athletes and people who work out are at greater risk for iron deficiency because they lose iron through sweat and through their intestinal tract. Runners also rupture red blood cells when their foot strikes the ground. If you don’t get adequate nutrition and enough iron-containing foods, your risk for iron deficiency anemia goes up. This is especially true for younger women who are still having menstrual periods. Iron deficiency anemia causes excessive fatigue and reduces exercise performance.
Exercise and Nutrition: The Bottom Line?
Calculate how many calories you need based on your height and activity level, and don’t cut back by more than 500 calories a day when you’re trying to lose weight. Make sure you’re getting a nutritionally-balanced diet that contains adequate amounts of the essential macronutrients – protein, carbs and fat, and don’t overtrain. To maximize the number of nutrients you get when you’re eating less to lose weight, eat whole foods such as fruits and vegetables and lean sources of protein rather than processed foods that lack nutrition. Don’t increase your risk for health problems by being too aggressive with exercise and calorie restriction.
References:
Am Fam Physician. 2000 Jun 1;61(11):3357-3364.
J Am Diet Assoc. 2005 Jun;105(6):975-8.
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