Intermittent Fasting: Benefits and Drawbacks

Mar 7

Written by INNER G

What intermittent fasting actually is

Intermittent fasting (IF) is a way of eating that switches between fasting and eating windows. Most diets tell you what to eat. IF mostly cares about when. People have fasted for religious and cultural reasons for centuries, and lately it's caught on for its possible health benefits.

The common versions:

16:8. Fast for 16 hours, eat within an 8 hour window.
5:2. Eat normally five days a week and keep calories to 500 to 600 on the other two.
Alternate day fasting. Fasting days and eating days take turns.
One meal a day (OMAD). All of the day's calories in a single meal.

What the research says it can do

Weight loss. A shorter eating window tends to mean fewer calories, and IF may help your body get better at switching to fat for fuel. A 2018 meta analysis of randomized trials found intermittent fasting led to about the same weight loss as cutting calories every day (Cioffi et al., 2018). So it works, but it isn't magic. It's mostly another way to eat less.
Insulin sensitivity. Studies suggest IF can lower insulin levels, which may lower the risk of type 2 diabetes (Patterson & Sears, 2017). In head to head trials the drop in fasting insulin was small, though, and only slightly better than regular dieting (Cioffi et al., 2018).
Brain health. Fasting may help brain function by raising brain derived neurotrophic factor (BDNF), which is linked to better cognition and protection of nerve cells. Most of this evidence comes from animal studies so far (Mattson et al., 2018). In theory that could lower the risk of neurodegenerative diseases like Alzheimer's.
Longevity. In animal research, IF may extend lifespan by improving how cells repair themselves. A review in the New England Journal of Medicine explained that fasting switches on autophagy, which is the body's way of clearing out damaged parts of cells (de Cabo & Mattson, 2019). Whether that adds years to human lives hasn't been shown yet.
Inflammation. Chronic inflammation is tied to a lot of diseases, heart disease and cancer included. A meta analysis of 18 trials found IF lowered C-reactive protein, a common inflammation marker, by a small amount (Wang et al., 2020).

The downsides

Hunger and fatigue. The first couple of weeks can be rough while your body gets used to the fasting window. Headaches, irritability and low energy are common.
Losing muscle. Without enough protein and some resistance training, IF can cost you muscle. Eat enough protein and keep strength training, and you cut that risk down.
Disordered eating. For some people, especially anyone with a history of eating disorders, IF can bring back unhealthy patterns.
It isn't for everyone. If you have certain medical conditions, you're pregnant, or you train hard most days, talk to your doctor before you try it.

Should you try it?

IF can work well for managing weight and general health, but it's one option, not a rule. The best eating plan is the one you'll actually stick to, and that fits your goals and your week.

Before you start, think about how active you are, what your schedule looks like and any health conditions you already have. Pay attention to how you feel, and make the meals you do eat count. They still need to be balanced and give you the nutrients you need.

References

Cioffi I, Evangelista A, Ponzo V, et al. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. Journal of Translational Medicine, 16(1):371. PubMed
Patterson RE, Sears DD (2017). Metabolic Effects of Intermittent Fasting. Annual Review of Nutrition, 37:371-393. PubMed
Mattson MP, Moehl K, Ghena N, et al. (2018). Intermittent metabolic switching, neuroplasticity and brain health. Nature Reviews Neuroscience, 19(2):63-80. PubMed
de Cabo R, Mattson MP (2019). Effects of Intermittent Fasting on Health, Aging, and Disease. The New England Journal of Medicine, 381(26):2541-2551. PubMed
Wang X, Yang Q, Liao Q, et al. (2020). Effects of intermittent fasting diets on plasma concentrations of inflammatory biomarkers: A systematic review and meta-analysis of randomized controlled trials. Nutrition, 79-80:110974. PubMed