By Brian B. Parr, Ph.D., ACSM Certified Clinical Exercise Physiologist
What you eat is an essential part of achieving and maintaining good health. What you may not know is that how and when you eat can be just as important. This is especially true if your goal is to lose weight, but changing the way you eat also can slow the aging process and reduce your risk of cancer and other chronic diseases. Ongoing research and practical experience suggest that eating more slowly and incorporating periods of fasting can help with weight control and improve your health.
Eating less is an important goal for losing weight and keeping it off. One effective way to limit the amount of food you eat is to eat more slowly. Perhaps your mother admonished you to slow down at meals when you were young. This was good advice, for both practical and physiological reasons.
When you eat, your stomach fills, triggering the release of hormones that signal your brain to reduce your appetite. The result is that as your stomach fills, you feel less hungry. Eating quickly, like many of us do, allows you to take in more calories before your brain gets the message that you are full. Practically speaking, eating slower means you will eat fewer calories during mealtime. If you slow down at meals, you start to feel full before you eat as much. Research shows that this can lead to lower calorie intake during the meal. In addition to controlling how much food you consume, eating more slowly is a good way to enjoy meals, both the food and the company, more fully.
Another approach is to extend the time between meals or limit eating to fewer hours per day. This form of fasting may affect your metabolism in ways that can help with weight control and improve your health. Restricting when you eat has been shown to have multiple health benefits from weight loss to reducing the risk for cancer, diabetes, and heart disease. There are two main ways to incorporate fasting into your diet – intermittent fasting and time-restricted eating.
Intermittent fasting is an eating pattern in which you have some days or times of day that you don’t eat. This could mean a day or more without eating each week or month. An example is the 5:2 model, in which you eat your normal diet for five days and then spend two, water-only fasting days per week. While this is effective for modest weight loss and improved glucose and lipid metabolism, it isn’t easy to do.
Time-restricted eating, in which you limit your eating to a 4 to 8 hour period each day with a 16–20 hour fast, may be easier to follow. In the popular 16:8 plan, you eat only during an 8-hour period and fast for 16 hours. The concept of not eating between meals, especially between dinner and breakfast, isn’t new, but research shows that having a longer fasting period each day may help you lose weight, without counting calories. Even without this evidence, adopting a fasting period between dinner and breakfast, which should be about 12 hours, seems prudent. At the very least, it will keep you from snacking in the evening, which so often involves unhealthy choices.
Intermittent fasting and time-restricted eating are thought to improve health by giving tissues time for growth and repair. For hours after you eat, your cells are processing the nutrients you consume. But cells also need time to repair damage to prevent abnormal function and growth. This can help prevent cancer development, reduce the risk of heart disease, and slow the cellular aging process. These processes are most active when your cells are not processing the food you eat, which is why longer periods without food are thought to be beneficial.
The time of day you eat may matter, too. Your body follows circadian rhythms that dictate cellular growth and repair, hormone levels, and brain activity. Most simply, this is a sleep-wake cycle, in which you are active and eating during the day, with growth and repair occurring at night while you sleep. There may be a benefit to confining your eating to earlier in the day so that the nutrients from your last meal are absorbed, processed, and stored before you go to sleep allowing that time to be dedicated to restorative processes. You can do this by eating your largest meal at lunch rather than at dinner.
You also need to consider the interaction between eating, exercise, and sleep. Intermittent fasting alone won’t make you any healthier if you are eating a poor quality diet, not exercising, and not getting enough sleep. In fact, inadequate sleep can disrupt your circadian rhythm diminishing the benefits of a healthy diet and exercise. We have long known that eating well, exercising daily, and getting adequate sleep are a winning combination for good health; eating more slowly and restricting your eating to certain times of day or days of the week may make those efforts even more effective.
Brian B. Parr, Ph.D., is an ACSM Certified Clinical Exercise Physiologist and Associate Professor in the Department of Exercise and Sports Science at the University of South Carolina Aiken.