Scientists now know why restricting caloric intake increases life span, although it's complicated and involves a variety of chemical pathways related to the body's utilization of energy. It seems also that if the body's attention isn't devoted so exhaustively on metabolizing food, it can pay more heed to housekeeping issues like ridding the body of plaques and other waste products. One genetic player in this complicated charade is the gene mTOR, found in both mouse and man, which acts as a traffic signal for directing energy consumption.
But the science behind CR, as it is known, may be far more simple. Eating itself, and processing associated nutrients, and growing, turns out to age cells considerably. We work hard to process our food, and our cells spew out a lot of toxic free radicals in the process. This is why we are told to eat more colorful fruits and veggies, whose antioxidants neutralize/scavenge the free radicals in food. But even eating more nutrients may not be as efficacious as eating less in general.
Now, the average person does not regard favorably the advice to cut down on the amount of food she eats. And why would she? Nobody likes restrictions. But what if you were told to reduce your amount of daily exercise? Now that would get your attention, would it not? If you are a fitness enthusiast, and more and more people fit the description - cramming an hour of daily exercise into an otherwise hectic schedule even if it means awaking at the crack of dawn or running at night with a headlight affixed to your forehead - you are likely moving in excess of fitness recommendations and also burning more calories than you need to maintain body weight, and are therefore taking in more food than you otherwise wood. The extra food you eat to refuel after your run or session at the gym generates free radicals, and exercise generates them too.
Consider that following the exercise guidelines and engaging in 30 minutes of cardiovascular fitness 5 days a week translates into running 15 miles per week at the relatively slow pace of 10-minute miles. Each mile run or walked burns 100 calories, so just meeting the exercise guidelines results in a caloric deficit of 1,500 calories, which you'll likely take in, within an hour after exercise, in a protein/carb mixture, if you follow fitness gurus.
I'm not suggesting you stop working out as a way of reducing caloric intake by 1,500 calories, I'm simply saying that if you are the type that feels unfulfilled unless you run 40 miles per week (4,000 calories) or does some crazy combination of biking and swimming and tennis and basketball, which likely causes you to burn thousands more calories than you otherwise would, that if a week passes by that you're not able to exercise so compulsively you not feel guilty about it, since you'll also be reducing your free radical production at the same time assuming your food intake falls as well, and it usually does. Fewer free radicals generated slows the aging process. See there's a bright side, or in this case a light side, to every scenario.
But on days when you're feeling like indulging, choose carbs over protein. New research out of Australia shows that, at least in mice, low protein, high carbohydrate (LPHC) diets can provide benefits similar to those obtained with calorie restriction, including lower cholesterol, improved insulin sensitivity, and life extension. What's more, mice on LPHC diets ate more food, but because their metabolism was higher than that of mice on the calorie-restricted diet, they did not gain more weight. And restricting calories did not provide any additional benefits in mice who ate high carbohydrate foods. As researchers concluded: "It appears that including . . . plenty of healthy carbohydrates in the diet will be beneficial for health as we age."
So don't deprive yourself. Eat sweets (read: whole fresh fruits) to your heart's content. And on the days when you work out, eat them some more.