Benefits and Drawbacks of Intermittent Fasting, According to Research

Illustration of intermittent fasting. Plate with food in the shape of a clock.

While it isn’t a magic cure for losing weight, research increasingly shows that intermittent fasting, which is known in the weight-loss world as time-restricted eating plans, has promise and may be a smart strategy for some people trying to lose weight.

But what’s really interesting about fasting are all the other health-related benefits researchers think it might have. Better chronic condition management. Disease prevention. Increased lifespan.

Dozens of studies have been published in recent years looking at the benefits of time-restricted eating or intermittent fasting. Increasingly, they’re gaining attention beyond the world of weight loss, especially among longevity advocates.

Can intermittent fasting help us live longer? Should it be a pillar of prevention? What other benefits could it hold?

For all its promise, intermittent fasting still has some limitations. While promising, studies show its benefits are far from conclusive (many longevity studies are only in animals and insects). Not everyone is a candidate for intermittent fasting because of medication issues, chronic conditions and other limitations (always let your primary care doctor know before you make significant changes to your diet). Finally, even where intermittent fasting has been shown to be beneficial, outcomes may not be any better than other approaches.

Fasting for Weight Loss
There are dozens of studies that show people lose weight when they fast intermittently. They also tend to lose fat, not just water weight if they follow a strict regimen. How does it work? Similar to traditional calorie-restricted diets, people who fast will generally eat fewer calories overall— unless they make up for the food they aren’t eating when they come off their fast.

Some studies have shown that intermittent fasting helps your body function better to aid in weight loss. Intermittent fasters have better metabolisms through lower levels of insulin and higher levels of human growth hormone and norepinephrine, which help the body break down fat and use it.

But is it any more effective than traditional dieting, where caloric intake is restricted? Maybe not. A 2023 study found that people who fasted lost less weight than people who took part in traditional diets (10 pounds vs. 12 pounds), though the difference wasn’t significant. Other studies have shown fasting participants lose lean muscle mass in addition to fat, which means their ability to burn calories efficiently was worsened by fasting.

Finally, studies have also shown that intermittent fasting wasn’t any more effective for long-term weight loss than traditional diets: People gained weight back once they stopped fasting.

Improved cellular health for increased lifespan
Our body cleans out damaged and dysfunctional cells and repairs, regenerates and produces new healthy cells through a process called autophagy. Fasting may increase the frequency of autophagy, resulting in a more efficient cell cleansing process. Evidence shows this may play a role in helping protect us from cardiovascular, inflammatory and neurodegenerative diseases, as well as potentially from cancer.

A Harvard study found a causal link between intermittent fasting and increased lifespan that researchers tied to this effect. Scientists think that fasting may keep our mitochondria — the energy-producing structures in cells — in a youthful state. Normally, our mitochondria become less able to process energy over time, leading to age-related diseases and general aging. Scientists used nematode worms for the study, but Heather Weir, the lead author of the research she conducted while at Harvard Chan School, concluded that the findings “open up new avenues in the search for therapeutic strategies that will reduce our likelihood of developing age-related diseases as we get older.”

Increased metabolism
Weight loss from fasting may not solely be due to intermittent abstinence from calories. Research is finding that fasting boosts metabolism—the conversion of calories and nutrients in foods to energy—and may result in greater loss of visceral belly fat that wraps around major organs as well as body fat. The same study, which was in humans, showed benefits to cholesterol profiles in the participants who fasted intermittently.

Fighting inflammation
Studies are also showing that fasting has the potential to reduce inflammation involved in chronic conditions including rheumatoid arthritis, multiple sclerosis, heart disease and cancer, in part by significantly reducing C-reactive protein, a key marker of inflammation. There are other ways to reduce chronic inflammation, without fasting.

Improving blood sugar and reducing insulin resistance
Several studies have found that intermittent fasting results in improved blood sugar control by lowering blood sugar levels and reducing insulin resistance. One study concluded that fasting is as effective at reducing insulin resistance as traditional reduced-calorie diets. This fasting benefit is especially valuable for people at risk of or managing diabetes to help keep blood sugar levels steady and from crashing or spiking.

Boosting brain health
Some evidence also points to fasting’s ability to lower risk for certain neurodegenerative disorders, at least in lab animals. Animal studies have also shown fasting enhances cognitive function through increased nerve cell generation — an exciting outcome that scientists theorize could one day potentially help protect against Parkinson’s and Alzheimer’s disease and improve outcomes for other neurodegenerative conditions.

Enhancing heart health
Fasting has the potential to drastically improve heart health by helping to lower blood pressure and decrease LDL cholesterol as well as triglycerides, which lowers the overall risk for coronary artery diseases. A review of several studies suggests that fasting may be a path for reducing total cholesterol levels and could lower diabetes risk for overweight individuals. Heart disease is the number one complication of heart disease.

Helping cancer prevention
In extremely early stages of research, alternate-day fasting in some test-tube and rat studies has been found to help block the formation of cancerous tumors or hinder their progression. It’s also been shown to increase chemotherapy’s effectiveness by making the cancerous cells more sensitive to treatment and helping protect normal cells. But studies lab studies frequently do not pan out in human studies.

All these studies paint a rosy picture of intermittent fasting and it’s health benefits, but there are also some drawbacks to consider.

Reducing calorie intake and missing meals can cause headaches, dizziness, nausea and insomnia. Fasting for weight loss can also backfire due to increased cravings and hunger pangs that can lead to weight gain. Being deprived of nutrients and caloric energy, the body reacts by increasing the hunger hormone ghrelin, released by an empty stomach to cue the brain that it’s time to eat.

Fasting also requires a nutrient-dense balanced diet on non-fasting days. But it can be easy to revert to unhealthy eating and over indulge as a natural reward for completing a fast. This can negate any weight loss benefit and limit any corresponding health benefits. There is also valid concern that frequent fasting has the potential to lead to eating disorders.

Fasting can also cause complications and danger if you have low blood pressure or take certain medications, including diuretics, blood thinners, blood pressure medications or meds that can affect your blood glucose levels like insulin or drugs for type 2 diabetes.

Fasting is also not recommended if you’re over 65 or have heart, liver or kidney disease, if you’re pregnant or breastfeeding, and for children, teens and young adults still developing. As with any restrictive diet, fasting should only be pursued after consulting your doctor and under his or her guidance.

Still, intermittent fasting shows promise. The challenge is teasing out its benefits, which most researchers acknowledge will requires more studies. In many human studies which show benefits, for example, it’s hard to determine what’s causing the benefit: weight loss or fasting.

There’s no question that we need more tools to help people lose weight. Obesity is causing significant increases in chronic illness and reducing overall lifespan. Fasting is one option to lose weight and reduce disease risk. 

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