Written by James Kingsland — Fact checked by Rita Ponce, Ph.D.
In recent years, intermittent fasting has gained popularity as a way to lose weight, improve health, and enhance performance.
Some studies suggest that this dietary approach may even extend a healthy lifespan without the need for the severe caloric restriction that classic anti-aging diets entail.
People who practice intermittent fasting eat few or no calories for anything from 12 hours a day to 1 or more days every week. The former technique is known as time-restricted feeding, whereas the latter is known as periodic fasting.
A recent review of the evidence suggests that this type of diet may help people with type 2 diabetes safely reduce or even remove their need for medication.
However, people should seek the advice of a diabetes professional before embarking on such a diet.
According to the Centers for Disease Control and Prevention (CDC), diabetes affects 34.2 million people in the United States, which equates to about 1 in every 10 people. In 2017, it was the seventh leading cause of death in the country.
People with type 2 diabetes have abnormally high concentrations of glucose in their blood, known as hyperglycemia.
Several factors may contribute to hyperglycemia in type 2 diabetes. These include reduced secretion of the hormone insulin, which regulates blood sugar levels, and reduced sensitivity of the body’s tissues to the hormone. Doctors refer to this reduced sensitivity as insulin resistance.
The condition can cause a range of severe complications, including kidney failure and blindness.
The goal of treatment for type 2 diabetes is to prevent or delay these complications and maintain the person’s quality of life.
Healthcare professionals encourage people with type 2 diabetes to exercise regularly, reach a moderate weight, and eat a well-balanced diet. However, most individuals also need to take drugs to lower their blood glucose levels.
Most of these drugs raise insulin levels, which the authors of the review say can have an unintended negative consequence.
“While this works to reduce hyperglycemia in these patients, the idea of treating a disease of insulin resistance by increasing insulin may be counterproductive, leading to the requirement of increasing amounts of medication over a long period of time,” they write.
People who take the drugs can gain weight and develop increased insulin resistance.
In addition, they can have raised levels of a hormone called leptin, which normally reduces appetite. This may suggest that they become increasingly resistant to this hormone, too.
They also have lower levels of a third hormone, called adiponectin, which usually counters diabetes and inflammation.
However, the authors of the review note that people can struggle to sustain daily calorie restriction for extended periods.
Some people may find it easier to practice intermittent fasting, which shows promise as a way to improve metabolic risk factors, reduce body fat, and promote weight loss in obesity.
To assess the evidence, the authors searched databases for review articles, clinical trials, and case series related to type 2 diabetes and intermittent fasting published between 1990 and 2020.
They concluded that this type of diet may improve several key features of the disease. The improvements include:
- reduced body weight
- decreased insulin resistance
- lower levels of leptin
- increased levels of adiponectin
“Some studies found that patients were able to reverse their need for insulin therapy during therapeutic intermittent fasting protocols with supervision by their physician,” they write.
For example, a case study followed three people with type 2 diabetes for several months after they started an intermittent fasting diet, which involved three 24-hour fasts per week.
Over the course of the study, all participants had significantly reduced levels of HbA1c, which is a measure of the average amount of glucose in the blood.
All three individuals lost weight and were able to stop their insulin therapy within 1 month of the start of the diet.
Crucially, they reported that they found the diet easy to tolerate, and none of them chose to stop the diet at any point.
“Within less than a month, they had significantly reversed their type 2 diabetes,” says one of the authors of the case series, Dr. Jason Fung, a kidney specialist who is an advocate for intermittent fasting.
“Even a year later, I think two of them are off all meds […], so doing ridiculously well for an intervention that is actually free, available to anybody, and has been used for thousands of years,” Dr. Fung tells the Weight Loss Motivation podcast.
The review authors also cited a clinical trial that randomly assigned 137 people with type 2 diabetes to either a continuous calorie-restricted diet or an intermittent fasting diet.
After 12 months, the two groups had similar reductions in their HbA1c levels. However, those in the intermittent fasting group lost more weight on average.
The review authors conclude that intermittent fasting may reduce body fat and insulin resistance not only by limiting overall calorie intake but also through “metabolic reprogramming.”
This reprogramming involves a switch from using glucose as fuel to burning fatty acids and ketones from the breakdown of fat stores.
By reducing body fat, they write, intermittent fasting may also improve sensitivity to leptin and adiponectin, which in turn improves appetite control and reduces chronic inflammation.
However, they conclude that this kind of diet may not be for everyone, writing:
“While alternate day fasting and periodic fasting have demonstrated efficacy in improving metabolic risk factors, it may be difficult to convince patients to give up or severely restrict calories for an entire 24-[hour] period. In America, we often eat three meals per day in addition to frequent snacking.”
They also caution that there may be safety issues with intermittent dieting.
For example, they say that healthcare professionals should closely monitor individuals who take medications that increase insulin levels. This is to prevent episodes of hypoglycemia, or dangerously low blood sugar levels, during fasting.
“[People with diabetes] should consult their physician prior to beginning an intermittent fasting regimen in order to allow for appropriate oversight and titration of the patients’ medication regimen during periods of fasting,” they write.
The authors note some limitations of the available evidence.
For example, many randomized controlled trials of intermittent fasting have not included people with diabetes. They call for more trials in people with this condition.
They also emphasize that most of the evidence for improvements in body composition and metabolic health with intermittent fasting comes from research in animals.