Wrong Exercise Can Hinder Weight Loss
Conventional weight loss advice says, “Just eat less and exercise more,” but it is usually given by someone who never needed to lose weight. What you eat, how foods are combined, and when you eat are just as important as how much you eat. Exercise also is not as simple as conventional advice implies. Just as with carbohydrates and fats, all types of exercise are not created equal. Although exercise routines are not my areas of expertise, having read the experts, it seems to me that how much and what kind of exercise is best for YOU is as much an individual matter as what, when, and how much you eat. There actually are types and amounts of exercise that cause fat deposition rather than fat burning.
There are three types of exercise: aerobic (also called cardio), muscle building (such as weight training), and moderate exercise (also called brisk activity). Aerobic exercise receives the most attention because it strengthens the heart muscles, helps the lungs and is beneficial for most people. (1) However, if done to excess or without sufficient food, aerobic exercise can be physically stressful and induce adrenal hormone production which causes the body to deposit rather than burn fat. If done without eliciting the release of adrenal hormones, it promotes weight loss very effectively because it boosts your metabolic rate for about 36 hours after exercising, thus causing you to use more calories regardless of your activity for the next day and a half. (2) If your insulin levels are low and stable during that time, those burned calories can come from stored body fat.
The definition of aerobic exercise is exercise that is strenuous enough to cause your heart to reach a target rate determined by your age. To calculate your target pulse rate, subtract your age from 220 and then multiply that number by 0.75. (3) There are pulse rate monitoring wrist watches that can be worn during exercise to easily monitor your pulse, either to keep it at the target rate for aerobic exercise or to keep it in an optimal range for fat burning, which is lower.
Muscle building exercise is also high intensity exercise and can lead to fat deposition if done to excess. However, increasing one’s muscle mass in the correct way – without causing the release of adrenal hormones – will raise your metabolic rate overall because muscle tissue consumes more energy than fat. Indeed, muscle loss as a result of dieting is often a reason that people cannot maintain their goal weight. They require less food after their diet than they did originally because they lost muscle while dieting. You can avoid muscle loss while losing weight by having sufficient protein intake (for women - 50 to 75 grams or 7 to 11 units per day; for men - 75 to 100 grams or 11 to 14 units per day (4)) and by doing exercise that builds muscle. For best results, strenuous muscle building exercises such as weight training should be done every other day because the recovery day between exercise days is the time when muscle fibers are built.
Eat before you exercise.
|In my opinion, moderate exercise (also called brisk activity) does not receive the respect from most exercise experts that it deserves. Perhaps this is because no special equipment or advice is needed. There is nothing to sell when a person takes up walking, but those who walk several times a week are most successful at maintaining weight loss after a diet.
Walking is often touted as the best way to lose fat (5) perhaps because it is near-impossible to walk too fast to induce an adrenal hormone response that turns off fat burning. In addition to moderate exercise being the best way to burn body fat, it also builds muscle, although you won’t end up with bulging biceps as you might from weight training. Another extremely important effect of moderate exercise is that it decreases leptin resistance. (6) (Leptin is the master hormone for the self-regulation of a healthy level of body fat. See the “Lose Weight by Controlling Your Hormones” page of this website for more about leptin resistance).
Formal metabolic activity tests exist that determine an individual’s optimal exercise pulse rate for fat-burning. Rather than having a test, Dr. Cheryle Hart says you can approximate your best fat burning zone by leisurely walking or bicycling, and that if you cannot carry on a conversation without sounding winded, you have exceeded that zone. (7)
Some people err on the side of too little exercise and benefit from adding a sensible exercise regime to their healthy eating plan. Always check with your doctor before starting an exercise program especially if you have been sedentary. Dr. Hart recommends starting with 10 minutes of moderate activity such as walking per day for the first week and increasing your time by two minutes per week. If you need motivation to take up exercise, consider these extra benefits. Moderate exercise is good for us in many ways in addition to burning fat: it relieves stress physically, helps remove your mind from distressing thoughts, releases endorphins in the brain (8), and gives you a chance to do something nurturing for yourself.
So what is the right amount and type of exercise for you? How can you listen to your body to determine this? It helps to understand the physiology of how your body supplies energy when you do strenuous exercise (aerobic or muscle building exercise). First, you burn whatever glucose is in your blood from a meal or snack eaten during the previous hour. Then your body converts glucose stored in the muscles and liver in the form of glycogen into glucose. We only have enough stored glycogen to supply us with fuel for about 20 minutes of intense exercise. Because fat cannot be converted to glucose rapidly, after the glycogen is gone, our bodies begin converting muscle protein into glucose.
If you exercise moderately, the fat conversion process is able to keep up with your glucose needs so fat will be burned. (9) Thus, the best way to lose fat is to keep your insulin levels low and stable (so you are in the fat-burning mode) and exercise moderately by walking, gardening, cleaning house, or leisurely bicycling. Dr. Hart says, “If exercising makes you hungry, it means you have used up your glucose and glycogen stores. Most likely you started burning muscle. An important thing to remember is that you don’t get hungry when you are burning fat.” (10) Thus, hunger after exercise is how your body tells you that you were exercising too hard to burn fat.
In The Insulin Resistance Diet, Dr. Hart recommends limiting strenuous exercise to no more than 25 minutes per day to avoid losing muscle mass. (11) She says that a mere 12 minutes of aerobic activity six days a week or 25 minutes three days a week is enough to increase your resting metabolic rate all week long. She advises doing stretching exercises or brisk activity (moderate exercise) if you want to exercise more than 75 minutes a week and recommends house cleaning, gardening, walking, and moderately paced swimming or bicycling as excellent ways to burn fat.
Although it is counter-intuitive to the “calories in with food, fat out with exercise” model you may have been living by, exercise without food can undermine efforts to reduce body fat. When you engage in strenuous exercise before breakfast or after work but before dinner (or at least a linked-and-balanced snack), your body releases adrenal hormones to cause the breakdown of glycogen in the liver so you have sufficient fuel for your exercise. (12) These adrenal hormones increase blood sugar levels which causes the release of insulin which can, if excessive, result in fat storage. The hormonal response to exercise without food and prolonged strenuous exercise is the same. After your glycogen stores are used up, fat is not mobilized to be burned for energy, but rather muscle mass is broken down for fuel. Since muscle has a higher metabolic rate than fat, if you lose muscle mass due to over-exercise, your overall resting metabolic rate will decrease, making it more difficult to lose weight.
In The Feel Good Diet, Dr. Hart tells about a patient of hers who was a fitness trainer and could not lose weight in spite of following a good linked-and-balanced eating plan. Dr. Hart prescribed a test to determine her best fat-burning zone, and the results showed that she should be exercising at a pulse rate of between 100 and 122 beats per minute for best fat loss, which was 30 to 40 beats per minute less than she usually maintained during exercise. When she began doing all of her exercise at the lower pulse rate, she lost 15 pounds in the next month. (13)
In summary, listen to your body about exercise just as you do about what you eat. Be alert for becoming winded during moderate exercise and slow down if you do. Consider buying a pulse monitoring wrist watch to make sure your pulse is where you want it when you exercise. For moderate exercise your pulse should be well below the target range for aerobic exercise and should remain in a good fat-burning range. If your exercise program makes you hungry, you probably are burning muscle rather than fat; diminish the intensity and time. If you usually get hungry after exercise, have a balanced protein and carbohydrate snack routinely before you exercise to avoid setting off the hormonal cascade that leads to storing fat. Eat properly to keep your insulin level low and stable (which keeps you in the fat burning mode) and make much of your exercise moderate. By applying these principles to your exercise program, you should be able to achieve good fat loss and a healthy weight.
1. Some people need to first strengthen their heart with more moderate exercise which promotes weight loss. Then they can add strenuous aerobic training after it will no longer interfere with weight loss. See the story about a patient of Dr. Hart’s near the end of this webpage.
2. Hart, Cheryle R., MD and Mary Kay Grossman, RD, The Insulin Resistance Diet, (New York: McGraw-Hill, 2001, 2007), 192.
3. Ibid, 193.
4. Ibid., 183.
5. Ibid., 179.
6. Galland, Leo, MD, The Fat Resistance Diet, (New York: Broadway Books, 2005), 122.
7. Ibid, 181.
8. Hart, Cheryle R., MD and Mary Kay Grossman, RD, The Insulin Resistance Diet, (New York: McGraw-Hill, 2001, 2007), 189.
9. Hart, Cheryle R., MD and Mary Kay Grossman, RD, The Feel-Good Diet, (New York: McGraw-Hill, 2007), 177-178.
10. Ibid, 156.
11. Hart, Cheryle R., MD and Mary Kay Grossman, RD, The Insulin Resistance Diet, (New York: McGraw-Hill, 2001, 2007), 192.
12. This is why I felt less hungry after exercise while on a low-calorie diet and also was, ironically, part of why I could not lose weight on a standard low-calorie diet weight loss diet.
13. Hart, Cheryle R., MD and Mary Kay Grossman, RD, The Feel-Good Diet, (New York: McGraw-Hill, 2007), 180-181.