Exercise & Fat Loss

The guidance most often given to people seeking to lose weight is to eat less and exercise more. This is wonderful advice for the couch potatoes who get motivated only during the Super Bowl or while watching “Rocky” marathons.   Bodybuilders know that exercise and diet are key ingredients to their success in reducing body fat down to the lowest possible level. Never is it questioned among those who practice a dedicated lifestyle whether the dual approach of diet and exercise aid fat loss. Acknowledging that both work in fat loss, medicine and science are aggressively investigating exactly how this happens.

 Is Starving Away Fat the Answer?
At the most basic level, fat loss occurs when energy intake (calories consumed as food and drink) is less than energy expended (metabolic rate and exercise).1 Dieting decreases the number of calories consumed and exercise increases the number of calories burned; seems simple and many assume the equation ends there. If fat loss were merely a matter of dropping calories, then slimming down would be a simple matter of just starving away the fat. Bodybuilders know this is not the case. Lower the calories too far and your energy drops until getting through the day is a challenge due to persistent fatigue and lethargy. Additionally, not only does weight loss slow down until it seems to stop, much of the weight loss appears to come from muscle rather than fat.2
  It is really a shame that severe dieting carries so many negative side effects, as it’s much simpler to cut calories than to burn more. Hundreds of calories can be dropped by switching to diet soft drinks or refusing dessert. In contrast, a half hour on the treadmill or a fairly intense session in the gym can be negated by a couple of cold beers.
  Beyond the immediate impact on energy balance (calories in versus calories out), dieting and exercise affect the body’s metabolism, which affects the balance between fat storage and fat burning.3 Overall metabolism includes both the resting metabolic rate and activity-related energy expenditure; in other words, the number of calories burned while resting and while working.
 Metabolic rate is controlled to some degree by a number of hormones circulating through the bloodstream. In addition to the rate at which calories are burned, it’s important to consider what substrate (type of calories— fat vs. carbohydrates) is burned. Using up sugar stores (glucose and glycogen) forces the body to catabolize (break down) protein, including muscle mass, in order to provide amino acids that are converted into glucose through a process known as gluconeogenesis.

 Exercise and Fat Burning
A recent paper reviewed many of the effects of exercise on the storage and oxidation (calorie burning) of dietary fat.3 Exercise burns calories, but the intensity, duration and type (aerobic vs. resistance training) of exercise determines not only the number of calories burned, but also what percent of those calories come from fat. The more intense the exercise, the more total calories burned. However, there is a bell-shaped curve in regard to the percent of those calories burned coming from fat. Moderate-intensity exercise, defined as 65 percent of VO2 max, burns the most fat.4 VO2 is not measurable in the gym, but 65 percent VO2 equates to 74 percent maximal heart rate (220 minus age times 0.74). For a 30-year-old, this would be exercising at a rate that maintains the pulse at 140 beats per minute.
  The fat burned during exercise comes from two sources: stores contained within muscle and fatty acids circulating in the blood. Fatty acid levels in the blood appear to be able to modulate the degree of fat oxidation (burning). When a high-fat meal is eaten 90 minutes prior to exercise, fat oxidation is increased.5 Conversely, a low-fat diet decreases lipolysis and fat oxidation.6 This might be explained in part by the fatty acid-glucose cycle— a relationship describing fatty acids’ ability to decrease glucose uptake and glucose oxidation in the presence of high fatty acid levels.7 A long-term, high-fat diet changes the body’s physiology, causing it to burn fat more so than compared to a high- carbohydrate diet.
  A great part of the benefit of exercise, relative to fat loss, comes not from the immediate calorie burning due to the increase in activity, but to the increase in fat burning during recovery. In contrast to the immediate effect of exercise, which had shown differences based upon intensity, the delayed effects of exercise on fat metabolism are based upon the total amount of exercise.8-10 In other words, relative to delayed fat burning, you get the same benefit working half as hard and twice as long, as you do working twice as hard and half as long.
In one experiment, researchers learned walking at 60 percent of VO2 for an hour increased dietary fat burning significantly for the next 20 hours.10 In other studies, it was determined that 30 minutes of walking burns approximately 25 grams of fat over the next 12 hours, about half during the exercise, the remainder during the 12 hour recovery period.11,12
  Both the immediate and delayed fat metabolism effects of exercise offer clear benefits, but what about long-term benefits in people who adopt an exercise-based lifestyle? Unfortunately, much of the research depends upon aerobic exercise (running, cycling and aerobics), but similar effects have been noted with resistance training, though to a lesser degree.