Two diets that have received a lot of coverage in the popular press recently are intermittent fasting and a ketogenic diet. Depending on what you hope to achieve through dieting, one or the other of these may help you reach your goal. To begin, let’s consider what each of these consists of and what they do to your body when you practice them.
Intermittent fasting means that sometimes you eat as you normally would, and sometimes you don’t. There are a wide variety of possibilities for intermittent fasting.
- Alternate day fasting: Eat normally on one day and then severely restrict calorie intake on the next. Rinse and repeat.
- The 5/2 diet: Eat normally on five days of a week and severely restrict calorie intake on the other two days. Keep this up long term
- The 16/8 diet: Restrict consumption of calories to an 8-hour window every day. This amounts to 16 hours of fasting every day and 8 hours of unrestricted food consumption. Make this a lifelong habit.
There are other possibilities, but the above three are representative. In all cases, the fasting interval shifts your body’s metabolism from being glucose-based to being ketone-based. This means that any practice of intermittent fasting has in fact put you on a keto diet.
Of the various flavors of intermittent fasting diets, the 16/8 diet is probably the easiest to stick to long term. You are probably already accustomed to fasting while you are asleep, so all it requires is that you refrain from eating right after arising in the morning and similarly avoiding food for the last few hours before you retire at night. I have written about the 16/8 fasting diet here.
There are several ketogenic diets, such as the Adkins diet, the South Beach Diet, and others, that are designed to shift your body into a state called ketosis. These diets do not recommend any kind of fasting, but instead call for the drastic reduction of the amount of carbohydrates that you consume, replaced by a high proportion of fat and a greater than normal amount of protein. The keto diets are primarily weight loss diets rather than health enhancement diets. They cause your metabolism to shift from the normal glucose burning mode to a ketone burning mode, where the ketones are stored in body fat.
People who practice intermittent fasting, may also do it as a means of losing excess body fat. However, there are much more valuable benefits to intermittent fasting than a slimmer waistline. A recent review article that appeared in the New England Journal of Medicine surveys research that studied the effects of intermittent fasting on disease incidence and lifespan, both in experimental animals and humans. The researchers state, “Intermittent fasting elicits evolutionarily conserved, adaptive cellular responses that are integrated between and within organs in a manner that improves glucose regulation, increases stress resistance, and suppresses inflammation.” The studies covered show the benefit of intermittent fasting on a wide range of chronic disorders, including obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases.
Why might intermittent fasting lead to better overall health? For most of human history, food has not been constantly and readily available to our ancestors. Hunter-gatherer societies were intermittent fasters, not by choice, but by necessity. If the clan’s hunters returned home with little or no game, people did without. If no roots or fruits could be found, people did without. Our metabolisms were shaped by the fact that people might go long periods without food, shifting from a food-burning to a fat-burning mode. We still have that same metabolism today, even though for most of us in the developed world, three meals a day, plus snacks whenever we want, is the norm.
For adults, 50 years old and older, the disorders reduced by intermittent fasting (obesity, diabetes, cardiovascular disease, cancers, and neurodegenerative brain diseases), are the primary causes of death. To delay or even eliminate the chance of being affected by these disorders is an outcome much to be desired. It might even be worth changing lifelong eating habits that are not a good match for the way the human body was designed to work.