Could Intermittent Fasting Be The Fountain Of Youth?
There’s been a lot of buzz in recent years about the health benefits of fasting and calorie restriction. In fact, intermittent fasting was the top Google diet search trend in 2019. Proponents of these protocols have promised everything from weight loss (obviously) to anti-aging (we’re intrigued). We’re all for positive lifestyle changes — that’s a given. But before we say sayonara to our midnight snack, we want to know if it’s safe, effective, and scientifically backed. Here, we comb through the research and speak with the experts to get the — ahem — skinny.
Calorie Restriction vs. Dieting
From the flapper-favorite cigarette diet and the postwar cabbage soup scheme to the modern keto craze, Americans are intimately familiar with the fantasy of fad diets promising fast results. These diet plans typically focus on one goal: weight loss. Depending on the science backing it up, sometimes that translates to better health. Other times, it results in rebound weight gain and nutritional deficiencies.
While the idea of limiting calories to manage weight has been around for centuries, certain techniques have gained popularity in the past decade for their possible health and longevity benefits. Unlike diets, the practice of calorie restriction (CR) and intermittent fasting (IF) are aimed at promoting health and extending lifespan. Dropping pounds, meanwhile, may or may not be a fringe beneift.
Calorie Restriction vs. Intermittent Fasting
Now that we know the difference between diets and calorie restriction, it’s time to understand what separates calorie restriction from intermittent fasting. To answer this fundamental question, we turned to the National Institute on Aging (NIA), a division of the United States National Institutes of Health (NIH). Here’s how the NIA defines it:
- Calorie Restriction: Refers to “reducing average daily caloric intake below what is typical or habitual, without malnutrition or deprivation of essential nutrients.”
- Fasting Diet: Eating is severely limited or refrained from all together during certain times of the day, week, or month.
When it comes to fasting diets like IF, the NIA says that a “practical effect” may be consuming fewer calories “because there is less time for regular eating.” Common fasting regimens include alternate-day fasting or restricted eating windows that maintain a prolonged daily fasting state.
The Science of Calorie Restriction & Intermittent Fasting
In December 2019, Mark Mattson, PhD, a neuroscientist at the National Institute on Aging and a professor of neuroscience at Johns Hopkins University, and Rafael de Cabo, PhD, head of the NIA’s Aging, Metabolism and Nutrition Unit (AMNU), published an article in the New England Journal of Medicine that concluded:
Evidence is accumulating that eating in a six-hour period and fasting for 18 hours can trigger a metabolic switch from glucose-based to ketone-based energy, with increased stress resistance, increased longevity, and a decreased incidence of diseases, including cancer and obesity.
And that's just one piece of a growing body of research on the topic. “Numerous studies show that fasting and calorie restriction can improve our body composition (lean muscle mass to body fat ratio), lower blood glucose and insulin levels, increase growth hormone production, increase longevity, and reduce inflammatory markers,” says Jennifer Hanway, a board certified holistic nutritionist and personal trainer.
Let’s break that down:
- Body Composition: Having a favorable lean muscle mass to body fat ratio has been proven to ward off chronic diseases, improve posture, and strengthen joints and bones.
- Blood Glucose & Insulin Levels: Keeping these in check lowers your risk of obesity, diabetes, and heart disease. It also helps in healing from injury, illness, and even aesthetic procedures.
- Growth Hormone Production: Release of growth hormones are necessary to maintain healthy tissues and organs.
- Longevity: Calorie restriction has been shown to increase lifespan in lab environments. Human studies suggest positive impacts on brain health and cognition, blood pressure, and resting heart rate.
- Inflammatory Markers: Studies of human immune cells show that fasting lessens chronic inflammation and has no adverse effect on the immune system overall.
Scientists suspect that we’re evolutionarily wired to function optimally when alternating between periods of feast and famine. When we eat, the body releases insulin to help our cells process the glucose in our blood. Some excess glucose is stored in the liver as glycogen, while the rest is converted to fat. After 12 hours of fasting, we start tapping those glycogen reserves. After 18 hours, our fat cells begin sending fat to the liver to convert into energy. This releases ketone bodies — energy molecules that have been credited with improving neurological function, promoting cellular regeneration, fighting cancer, and more. This process is known as metabolic switching.
Calorie Restriction & Longevity
When it comes to longevity, there’s a host of animal studies that suggests the promise of these restrictive eating protocols. Here’s a roundup:
- Rodent studies have shown that a 10 to 40 percent calorie reduction can result in longer lifespans with less incidence of disease — especially cancer.
- Studies involving the worm C. elegans show a fasting diet increased their lifespan by 40 percent.
- Ongoing NIH studies of rhesus monkeys have shown a decrease in age-related diseases (like cancer, diabetes, and cardiovascular disease) over 20 years. One study showed an increase in lifespan, while another did not.
But just because something works in worms or primates doesn’t mean it’ll hold true for humans. There is, however, some observational evidence to suggest that these protocols promote health. Taking that a step further, here’s a look at two recent human trials aimed at providing objective, quantitative results:
The CALERIE Study: The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE) study supported by the NIH followed 218 normal to slightly overweight individuals for two years. Test subjects were randomly divided into two groups:
- The calorie restriction group was told to reduce their daily intake by 25 percent
- The control group was told to follow their regular diet
So what happened to those in the CR group? Though they, on average, reduced their daily caloric intake by 12 percent instead of 25, subjects lost an average of 10 percent of their body weight and, for the most part, kept it off for at least two years after the study concluded.
As for overall health, the participants in the CR group:
- Lowered their cholesterol and blood pressure, which reduces risk of diabetes, heart disease, and stroke
- Decreased levels of inflammatory factors and thyroid hormones, which some studies suggest may translate into a decrease in age-related disease
No significant negative impacts were detected, though some participants experienced periods of anemia. Researchers concluded that the CALERIE protocol is safe under a doctor’s supervision.
The TREAT Study: The Time Restricted Eating As Treatment (TREAT) study conducted by researchers at the University of California San Francisco, examined 116 overweight or obese individuals for 12 weeks. Participants were randomly divided into two groups:
- The consistent meal timing (CMT) group ate three meals daily at set times
- The time restricted eating (TRE) group ate whatever they wanted, but only between 12 p.m. and 8 p.m.
The results, published recently in JAMA Internal Medicine, have caused some controversy because they show no statistically significant difference between the two groups. The study suggests that intermittent fasting for weight loss doesn’t work, with some of the participants in the TRE group even losing lean muscle mass.
These conclusions are being debated in the scientific community. Some experts say the research exemplifies why it’s so hard to study humans: Left to our own devices, we’re just not that consistent — even when given clear instructions. A number of study participants did not adhere to the exact eating requirements and some didn’t complete their surveys — both of which certainly impacted the findings. In many ways, these studies underscore the fact that we have much more to learn about the topic.
Intermittent Fasting & Skin Aging
While living longer, healthier lives is certainly promising, is it too much to ask that we look more youthful and vibrant to boot? Hanway says that some of these biological benefits can indeed affect our outer beauty.
For starters, IF may help delay the skin’s aging process. “Intermittent fasting can have skin benefits due to its lowering of blood glucose and insulin levels,” she says. “When blood sugar is high, it can cause glycation of the skin, in which the sugar molecules bind to the collagen and elastin in our skin, preventing it from staying firm and supple and contributing to premature aging.”
But that’s not all. As we mentioned earlier, IF and CR can improve the body’s natural healing processes — including the skin. “Intermittent fasting increases our rate of autophagy, or cellular ‘clean-up,’ which can help our skin to repair faster and improve protection itself from internal and external stressors,” Hanway shares. Cheers to having our cake (between 10 a.m. and 6 p.m., of course) and eating it, too.
The Risks of Caloric Restriction & Intermittent Fasting
From simple social challenges (sorry, I don’t eat past 4 p.m.) and ‘rebound’ overeating to a slower metabolism, fatigue, moodiness, and nutrient deficiencies, the list of possible complications from IF and CR protocols is long. “Intermittent fasting can be very stressful on the body and can be especially challenging for women, as they have a more complicated endocrine system than men,” Hanway cautions. As she explains, IF and CR can also lower metabolism and thyroid function, if taken to extremes.
While we’ve discussed the potential benefits as far as aesthetics are concerned, it can quickly go the other way. ‘When a diet is low in protein, healthy fats, and micronutrients, it shows up as thinning or loss of hair, weak, brittle nails, and premature aging of the skin,” Hanway warns. To avoid such complications, calorie restriction and intermittent fasting should only be embarked upon under the supervision of a professional. It's crucial to maintain a healthy diet, including a mix of carbohydrates, protein, and healthy fats.
While more research is needed, most experts agree that some forms of calorie restriction and intermittent fasting can be beneficial in the right candidates. For those interested in experimenting, Hanway offers a more moderate approach. “Many of the benefits of IF can be gained from a less restrictive form of fasting called Time Restricted Eating (TRE),” she explains.
With this scheduled protocol, you can maintain a relatively normal eating schedule. “Rather than jumping in the deep end with a long fast or fasting during the day, I recommend aiming for a minimum of 12 hours overnight between dinner and breakfast and three to four hours in-between meals,” she shares. “You can then gradually extend your overnight fast to up to 16 hours, but I do not recommend any longer than that.”
Talk to your doctor or nutritionist to determine if this kind of eating plan may be right for you.