There are lots of diets out there: plant-based, Paleo, gluten-free, sugar-free, high-fat, low-fat, macrobiotic, "clean eating," starch-based, and many more. Proponents of each diet see the others as rivals that they must compete against for new followers. This leads to a lot of mutual disparagement. For example, plant-based dieters denigrate the Paleo Diet as carcinogenic, while anti-sugar zealots denounce fruitarian diets as an express ticket to future Type 2 diabetes. There is one rival, however, that all of the popular diets—or diet cults, as I call them—share: exercise.
The diet cults have a common interest in playing down the importance of exercise. After all, they are in the business of convincing people that perfect health is attainable entirely through the perfect diet. To acknowledge the health benefits of exercise is to acknowledge the limitations of healthy eating. Paleo dieters have gone so far as to rename aerobic exercise "chronic cardio," as though it were some form of pathology.
Most diet cults do not foster such extreme views, but virtually all of them do subscribe to the popular notion that the correct formula for healthy weight management is "90 percent diet, 10 percent exercise." It sounds good, but it's completely false. In reality, exercise has a far more powerful impact on weight management than does diet. Skeptical? Read on.
Exercise Prevents Weight Gain
In 2011, The New England Journal of Medicine published a large study in which researchers at the Harvard School of Public Health looked at the effects of food choices and lifestyle habits on body weight in a population of more than 120,000 adults over a period of 20 years. The average subject gained 16.8 pounds over this time span. Particular foods were found to contribute to weight gain, while certain other foods tended to reduce weight gain. But the impact of exercise on body weight was almost as great as all healthy food choices combined.
To avoid gaining any weight, the average participant in this study who did not exercise would have needed to increase his consumption of vegetables, fruits and whole grains, and reduce his intake of processed meats and sugary drinks. The average subject who did exercise could achieve the same result simply by eating fewer potato chips.
Other research has shown that a vigorous exercise habit, such as the runner's lifestyle, prevents long-term weight gain almost completely, independent of diet. For example, a 2005 study conducted by researchers at Lawrence Berkeley Laboratory and involving more than 40,000 female runners found that runners in their 60s who ran at least 35 miles per week were only four pounds heavier than runners in their 20s who ran an equal amount. The runners in their 60s also weighed less than runners in their 20s who ran fewer than 24 miles per week.