If you consume more calories than you burn, you gain weight. Do the reverse and you lose weight. This formula seems simple enough, but contains a world of nuance that we are just beginning to understand. Eating fats, for example, works to satiate, which can reduce caloric intake, while carbohydrates and sugars can inspire hunger. And evidence is accruing that the timing of your meals can affect metabolism. When you eat may be as important as what you eat, or how much.
A study in the June 2012 issue of Cell Metabolism looked at two groups of mice. Both groups consumed the same number of calories. The only difference was one group ate whenever it wanted, day or night, while the other was allowed to eat only during an eight-hour daily span. The mice that ate whenever they wanted grew fatter, exhibited higher blood sugar, decreased insulin sensitivity, decreased motor skills and more fatty deposits on their livers.
This is one of many recent studies pointing to the benefits of a dietary regime called intermittent fasting, or IF for short. Many IFers, as they're called, combine IF with exercise during fasting periods, an approach called fasted training. Martin Berkhan, author of the Leangains blog, is grotesquely ripped, regularly eats ungodly amounts of cheesecake and has a Belieber-esque following of eager disciples. He advocates a schedule similar to that of the experimental group of mice in the above study: an eight-hour feeding window during which he eats whatever he wants, and a 16-hour fasting window, which he concludes with a workout before eating his first meal of the day, in early afternoon.
What's anecdotally interesting about IF and fasted training is how vocal practitioners are, not only about their killer abs but also benefits like increased mental clarity and productivity and a generally enhanced sense of well-being, while reporting how little they miss food while fasting.
An April 2013 study in the British Journal of Nutrition offers some of the most concrete support to date for the idea that IF can promote lasting weight loss. A group of overweight women followed an IF format called the 5-2 diet, in which they ate freely for five days and consumed a low-calorie diet the other two days of the week. The control group followed a conventional weight-loss diet of smaller portions of low-cal food on a typical, three-meals-a-day schedule. The 5-2 diet group lost significantly more weight than the control group and showed improved insulin sensitivity, which indicates a move away from a diabetic condition. One of the subjects told NPR's The Salt blog that she not only lost weight, but "felt quite refreshed and healthy" on the 5-2 schedule, and plans to "carry on" with it.
Obesity is a well-known precursor to many serious diseases, and slimming out of this category is clearly advantageous. But it seems there are more benefits to IF than weight loss.
Mark Mattson directs the Laboratory of Neurosciences at the National Institute on Aging and is a professor of neuroscience at Johns Hopkins School of Medicine. He studies the roots of age-related neurodegenerative decline, and diseases like Alzheimer's and Parkinson's. Lately his research has focused on the effects of intermittent fasting on these and other age-related problems.
Working primarily with rodents, his lab has found significant health benefits to both IF and exercise, both of which he views in an evolutionary context. In a recent article in Health Naturally magazine, Mattson wrote:
"From an evolutionary perspective, IF is normal and eating 3 meals a day plus snacks is abnormal. Going without food for most of the day or even for several days is a challenge that we are very capable of meeting. Similarly, humans are capable of quite remarkable amounts of physical activity, particularly endurance running, which has been an important factor in their evolution.Challenges such as IF and exercise are not only tolerable, but we thrive on them because they make our cells and organs stronger, and more likely to recover from injuries and illnesses."
Mattson's rodent experiments have shown that mild stresses like hunger and exercise can stimulate the growth of new brain cells, among other examples of cellular resilience. His lab has also linked IF to decreased blood pressure, improved recovery from stroke, decreased diabetic neuropathy, lowered cholesterol, decreased cancer rates, improved cognitive function and reduced inflammation in many parts of the body, including the lungs of asthmatics.
An IFer himself, Mattson rarely eats breakfast or lunch. His research and practice have turned him into a vocal critic of the food and drug industries for taking the low road with respect to public health. From his Health Naturally article:
"While the scientific evidence conclusively shows that IF is good for health, particularly in individuals who are overweight, health care providers rarely or never prescribe IF diets to their patients. Why? Sadly, the reason for this lack of effort by primary care physicians is that no one profits from IF prescriptions. The processed food and agriculture industries collaborate to produce and market energy-dense foods that include chemical additives that are addictive. ... Drugs are promoted by pharmaceutical companies with their implicit mantra: 'don't worry about getting a disease, we have a pill you can take for that.'"
Such claims may sound more like a diet guru hawking a book than one of the most frequently cited and highly respected researchers of his day. It's a sobering reminder of the frequent lag between medical research and dietary advice.
The calories-consumed-versus-calories-burned formula is not broken, but it certainly isn't as simple as it's often portrayed. And there is more than body fat at stake. Even though the medical establishment has yet to embrace IF, the good news is no prescription is required, and it might even save you money. By Mattson's estimates, IF can cut about 20 percent of your food bill, along with that stubborn belly fat.