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Healthy Weight
Article by The Harvard School of Public Health
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Low-Fat Weight Loss Strategies Don't Work For Most People
Low-fat diets are routinely promoted as a path to good health. But they haven't fulfilled their promise. One reason is that many people have interpreted the term "low-fat" to mean "it's OK to eat as much low-fat food as you want." For most people, eating less fat has meant eating more carbohydrates. To the body, calories from carbohydrates are just as effective for increasing weight as calories from fat.
In the United States, obesity has become increasingly common even as the percentage of fat in the American diet has declined from 45 percent in the 1960s to about 33 percent today. In South Africa, nearly 60 percent of people are overweight even though the average diet contains about 22 percent of calories from fat. Finally, experimental studies lasting one year or longer have not shown a link between dietary fat and weight.
Low-Carbohydrate, High-Protein Strategies Look Promising
Another increasingly common approach to weight loss is eating more protein and less carbohydrates. One widely publicized high-protein diet entails loading up on meat, cheese, fish, and eggs while dramatically cutting down or even eliminating carbohydrates. This may help you drop some pounds. But the long-term effects of this eating strategy--on weight as well as overall health--aren't yet clear.
Limiting carbohydrates can help avoid sharp spikes in blood sugar and insulin levels, and equally sharp declines in blood sugar. Keeping blood sugar at a relatively steady level may dampen the appetite. However, many high-protein, low carbohydrate diets are full of saturated and trans fats. These could significantly increase the risk of heart disease regardless of any actual weight loss. A restrictive high-protein, low-carbohydrate diet may also limit the consumption of important vitamins, minerals, and other nutrients found in banned carbohydrates such as fruits, vegetables, and whole grains.
Emerging evidence suggests that a more balanced approach that includes protein, carbohydrates, and fats has value as a weight-loss strategy. In a study conducted at Duke University, 51 healthy but overweight or obese volunteers were placed on a diet that included no more than 25 grams of carbohydrate a day, but that put no daily limit on calories. They also received counseling and support on nutrition and exercise. After six months, 41 of the volunteers were still following the program. This is a higher percentage than usually seen with people on low-fat diets. Mean body weight decreased 10.3 percent (or approximately 20 pounds) and the mean percentage of body weight that was fat decreased 3 percent. Cholesterol levels improved across the board, with decreases in LDL and triglycerides and increases in HDL.
In such high-protein, low-carbohydrate diets, the types of carbohydrates and fats is probably of critical importance for long-term health. A high-protein diet that emphasizes monounsaturated and polyunsaturated fats while limiting saturated and trans fats will invariably be better than one that includes saturated and trans fats.
Lessons from Losers
Since 1993, nearly 3,000 women and men have joined the National Weight Control Registry. This select "club" includes only people who lost more than 30 pounds and kept them off for at least a year. What was their secret?
- They exercised. Registry participants burn an average of 400 calories per day in physical activity. That's the equivalent of about an hour of brisk walking.
- They ate fewer calories. On average, registry volunteers consume about 1,400 calories a day. That's significantly less than the calories consumed by the average American. This doesn't mean, however, that you should aim for 1,400 calories a day. What's right for you is based on your weight, height, and activity level.
- They switched to lower-fat diets, cut back on sugars and sweets, and ate more fruits and vegetables.
Keep in mind that these are commonly used strategies, not hard and fast rules. In fact, one of the main take-home messages is that successful weight loss is very much a "do it your way" endeavor.
These findings are echoed in a survey of more than 32,000 dieters reported in the June 2002 issue of Consumer Reports. Nearly one-quarter had lost at least 10 percent of their starting body weight and kept it off for at least a year. Most chalked up their success to eating less and exercising more. The vast majority did it on their own, without utlizing commercial weight-loss programs or resorting to weight-loss drugs. Interestingly, the successful losers in the Consumer Reports survey tended to adopt low-carbohydrate/high-protein diets rather than low-fat diets.
What these two groups have in common is a focus on exercise and daily calories. In other words, they've learned to balance energy in and energy out in a way that leads to weight loss or weight maintenance.
So despite all the pessimistic prognostications about the impossibility of sticking with a weight-loss plan, these two surveys show that it's possible to lose weight and keep it off. Unfortunately, only a minority of people who try to lose weight follow the simple, tried-and-true strategy of eating fewer calories and exercising daily. For weight control, an hour of exercise a day may be needed.
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