People are really excited about not eating these days. There are several variations of fasting or intermittent fasting diets floating around. Some proponents even bristle at the term "diet." It's a lifestyle, they say... usually in all caps on Facebook and Instagram.
The short-term effects seem pretty good, and weight loss is common. But what about the long-term effects? Researchers are now taking a look.
In this rat study, researchers put subjects on an intermittent fasting plan consisting of every-other-day eating. In other words, one day of fasting, then one day of calorie-controlled eating. This was repeated for 3 months.
Note: The human equivalent to this is often called "alternate day" fasting, and a quick Google search shows that lot of folks are trying it.
- The subjects lost weight, but ironically gained abdominal fat, what some doctors call "central adiposity" in humans.
- The cells of the pancreas that release insulin showed signs of damage.
- Markers of insulin resistance were detected.
- Increased levels of cancer-causing free radicals were observed.
Researcher Ana Bonassa noted, "This is the first study to show that, despite weight loss, intermittent fasting diets may actually damage the pancreas and affect insulin function in normal healthy individuals, which could lead to diabetes and serious health issues."
This was the second study showing that popular fasting plans may have some serious drawbacks, especially for those that have adopted them as a "lifestyle" rather than as a temporary strategy. (Although previous studies show a boost in age-accelerating free radicals even during short-term fasts.)
In the first study, a more common IF approach was tested: eating only during a 4-hour window in a day. In that one, the subjects didn't lose weight, but did...
- Gain intra-abdominal fat
- Develop disordered-eating behaviors (binge eating)
- Develop insulin resistance in their livers
- Show signs of inflammation
- Display a "gene expression profile favoring lipid deposition." That means their genes started "preferring" to store more fat, especially in the belly.
In these studies, two different types of fasting were shown to really screw up how your body is supposed to make and manage insulin, which might lead to type-2 diabetes. Then there's that whole abdominal fat thing: the "pregnant belly" look usually seen with out-of-shape middle-aged men.
Now, this info will be hard to swallow for those who've adopted diets where they don't get to swallow much. That's because many of these fasting plans have an aura of religious fervor surrounding them. The true believers make militant vegans look rational.
Also, these fasting plans usually "work" in the short term: weight is lost. It's easy to get caught up in the short-term positives, especially if we don't know much yet about the long-term negatives. But we're getting there.
Yes, these were animal studies, but they should at the least serve to calm some of the mania surrounding fasting diets. Proceed with caution.
Note: Very short-term fasts, like one-day fasts or semi-fasts done once per week or so, probably don't have these same drawbacks and have been shown to be beneficial.
- European Society of Endocrinology. Could intermittent fasting diets increase diabetes risk? Fasting every other day to lose weight impairs the action of sugar-regulating hormone, insulin, which may increase diabetes risk. ScienceDaily. 20 May 2018.
- Kliewer KL et al. Short-term food restriction followed by controlled refeeding promotes gorging behavior, enhances fat deposition, and diminishes insulin sensitivity in mice. J Nutr Biochem. 2015 Jul;26(7):721-8. PubMed.