Intermittent Fasting: Facts or Another Fad?

Harvard Health is calling intermittent fasting (IF) a “promising” diet with emerging research and popularity in their article titled “Intermittent Fasting: The Positive News Continues”. For those who may not know, IF is a diet that encourages eating during certain times of the day, and refraining from eating—or fasting—other times of the day. Let’s break down this article through the eyes of Dietitian Tianna:

Credibility of the Source

Anything from Harvard should be trustworthy, right? Well, maybe not. The author of this article is a medical doctor with a degree in public health, however, she likely did not receive comprehensive nutrition education. Unfortunately, medical school requires very little or no nutrition education in the classroom at all. Registered dietitians on the other hand, like Dietitian Tianna, are the nutrition experts in our healthcare system. Another important thing to note is that Harvard is a business, and as such has an incentive to make its articles “clickable”. Toxic diet culture has no doubt influenced the content of this article to be centered around weight loss. 

Research Methods

The article discusses IF research in rats but admits that research in humans is far less robust. The problem with using rats to study IF is that we can’t get into the mind of the rats. We can’t ask them if they are experiencing cravings, struggling to focus at work, or have other side effects associated with not eating. Furthermore, food is restricted with rats; they aren’t just told not to eat during the period of fasting, they wouldn’t be able to even if they wanted to. We know that when humans go long periods without eating, like IF encourages, it sets them up for overeating or bingeing when food finally becomes available.

The reason there are so few human studies for IF is because it is an unsustainable diet. It is not easy to ignore your body’s natural hunger cues, because it is not natural! Biologically, we know that feeding our bodies throughout the day, guided by our internal cues, makes us feel and perform our best. 

One human study the article does reference followed a group of “obese” men over 5 weeks. First off, the way obesity is categorized is extremely flawed. Check out our BMI is BS blog post for more about this. Second, 5 weeks is not long enough to determine if IF is effective or sustainable long term.

Ironically, the article interviewed Dr. Wexler of the Massachusetts General Hospital Diabetes Center, who says this about IF: “’there is evidence to suggest that the circadian rhythm fasting approach, where meals are restricted to an eight to 10-hour period of the daytime, is effective.’ But still she recommends that people ‘use an eating approach that works for them and is sustainable to them.’

Red Flag Language

When discussing the background and history of IF, the article quotes Dr. Fung, “…for God’s sake, stop snacking.” Again, doctors are health professionals, but they are not nutrition experts. Dr. Fung’s quote is a huge red flag from a dietitian’s perspective. There are a million reasons why snacks are healthy, and for this doctor to reduce snacking to a flippant dismissal is a red flag. 

Misrepresenting Physiology

The article describes the mechanism by which IF induces weight loss as far more simple than it really is. It says, “Between meals, as long as we don’t snack, our insulin levels will go down and our fat cells can then release their stored sugar, to be used as energy.” Actually, our body uses glycogen stores, not fat cell stores, when we go without snacking between meals. We don’t want to rely on our glycogen stores all the time, because we need them to maintain a healthy blood sugar level through the night while we sleep. 

IF may cause weight loss. The issue is that fasting, or depriving your hungry body of food, is not sustainable. We know that with any diet-induced weight loss, you are likely to gain the weight back, and then some. This is called weight cycling, and it carries very real health risks including insulin resistance and metabolic syndrome.  

Harmful Tips

The article explicitly says “Avoid snacking or eating at nighttime, all the time”. Dietitian Tianna wholeheartedly disagrees. If you’re hungry before bed and do not eat, how do you think you will sleep that night? It is healthy for mind and body to give yourself that snack before bed. It is healthy to give yourself a snack any time of the day that your body asks for it.

The Bottom Line

There is a disclaimer near the end of the article that reads “…people with a history of eating disorders like anorexia and bulimia… should not attempt intermittent fasting”. Dietitian Tianna is an eating disorder specialist and says that this should not be taken lightly, nor should it be advertised to the masses. Most of her clients come to her not realizing they have diagnosable eating disorders. People may attempt IF, not realizing that they have had, currently have, or are at risk of an eating disorder. Attempting IF can trigger eating disorder behaviors, and that is the true harm.