There is a new diet in town, which, as we all know, is something that happens every couple of years. For the last several years, most diets that come and go have similar attributes with each other: limit processed and sugary foods, focus on whole foods and lots of vegetables, consume lean proteins, and eat small, frequent meals. There has been such a crossover for these attributes that my go-to answer for patients already pursuing a diet is, “Great, if that is working for you, go ahead and continue.” In other words, the minutia of the various diets didn’t matter as much as whether or not people were maintaining those basic tenets. The latest diet, however, breaks one of those longstanding rules which is to eat small, frequent meals. In fact, its main idea is to include hours or days of fasting to promote health and metabolism. Because it breaks one of our longstanding nutritional mantras, my simple answer to “carry on” doesn’t work. The next easiest opinion to give would be to declare it as rubbish, but my conscience wouldn’t let me do that without a little research. And darn if there isn’t some interesting research behind the process. Long story short, there just might be something to this, but maybe not for everyone. So, what exactly is intermittent fasting, is it safe for you, and could it possibly be worth it?
There are several different fasting patterns that have been labeled as intermittent fasting, but the commonality is usually at least a 16-hour span of not eating. Many will do this by making sure that they do all their eating within an 8-hour period each day (i.e. from 11am-7pm or from 12pm-8pm). A more extreme method is to eat little to no food for 2 out of 7 days of the week. It is thought that most people given the limited time to eat will simply eat less, but the science goes beyond a simple calorie save. The basic theory works off of the fact that when you eat, glucose is used as energy for about a 10 to 12 hour period following the consumptionof any food. After the 12 hours, when glucose stores known as glycogen are depleted, is when you will delve into your own stores of fat for use as energy. This use of your stored fat is then supposed to lead to weight loss.
In addition to the appeal of extra fat burning, proponents of intermittent fasting also point to studies possibly highlighting improvements in other health parameters. So far, many studies are on animals, but the results are promising. Fasting has been shown to improve biomarkers of disease, reduce oxidative stress, and preserve learning and memory, according to the National Institute on Aging (a division of the National Institute for Health (NIH). The NIH is working with the hypothesis that many of these findings might result from putting the body into a mild state of stress. This would be a similar response to exercise, which is also a stress to the body. With fasting, a stress is felt by all cells which are looking for energy to function and the body perhaps will adapt by enhancing its ability to cope with stress, and maybe even resist disease.
Interestingly, it has been this stress response to fasting that we have warned people against for decades now. Have you ever heard that people who skip breakfast gain weight? Unless you’ve been under a rock, you have. These breakfast skippers were intermittent fasters before it was even a thing and animal and human studies alike can be found that seem to say they gain weight by doing this. To make matters even more confusing, this side of the debate has a pretty good hypothesis too: fasting releases cortisol (our response to stress), cortisol sends out messages to store energy, therefore, increasing fat storage instead of burning through it.
I see only two ways to reconcile having two sides to this argument which is to either succumb to the fact that maybe, just maybe, not everyone’s metabolism works exactly the same way (note the sarcasm here because your friend that always orders dessert already answered this question for you). Maybe we don’t all have the same response to stress even, for example, do you gain weight during stressful periods, or do you waste away? Maybe intermittent fasting will be a breakthrough for some in weight management and health, but it could be a detriment to others. This is where long-term human studies will eventually help us out.
The other way to reconcile these two theories is to carefully weave the two together. I’ve consistently coached people for 15 years that once they eat after a fast, they will store those calories really efficiently. But now I’m here to concede that maybe if they are careful in what they consume after the fast, perhaps if they can continue to override their immediate desire for sugar or simple carbohydrates that they will be craving at that 16-hour mark, the efficiency in storage would be outweighed by the calories and fat burned during the fast. In other words, if you are going to try intermittent fasting, be mindful of how you break the fast. At the beginning, and maybe for a while, your body will be seeking easy carbohydrates (sugary and white foods). Your challenge won’t end with the fast, but will continue as instead you choose fiber-filled vegetables and lean proteins that won’t provide too many calories to efficiently store. Even proponents tend to coach intermittent fasting as follows: eat sensibly most of the time, eat nothing for an extended period every now and then, and indulge only on occasion.
So, if you are going to choose intermittent fasting as an option for your nutritional regime, I would highly encourage that you do so moderately. Choose one of the more modest fasts (fasting 16 hours) as opposed to days at a time, which put us into a whole other debate as we scoff in the face of years of evidence of weight loss resistance with yo-yo dieting (restricting and then not restricting calories). There are also a few groups that should avoid it all together including diabetics and hypo-glycemics, two groups that can have blood sugar crashes, which can lead to serious consequences. And, as a rule, everyone should inform their treating physician of diets they are pursuing, especially if you have an illness or you are taking a medication that you might not realize can be affected by food, or the lack thereof.
Diets come and go, but frankly, this concept is going to have bigger wings than the diets we have seen of late. We need more research. If you are going to try this one, make good, moderate choices, and still remember: limit processed and sugary foods, focus on whole foods and lots of vegetables, and consume lean proteins. These rules aren’t going anywhere.
Stay healthy & be well!
-Amy Whittington, NMD