The tradition of fasting goes back thousands of years, but more folks are trying it now than ever before. A growing body of evidence suggests that this ancient spiritual practice may also have big health benefits, particularly for those who are overweight or at risk for certain chronic conditions, including heart disease and diabetes.
Fasting is generally defined as the abstinence from some or all food or drink, or both, for a specified period of time. One look at the research, though, and you’ll quickly realize fasting can take many forms, which is confusing if you’re considering it for health reasons. The two most popular approaches to short-term fasts (also known as intermittent fasting) are alternating reduced- or zero-calorie days and significantly cutting calories two days per week (also known as the 5:2 diet). The main thing these approaches have in common is eating healthfully on non-fasting days.
Still wondering if fasting is right for you? Let’s take a closer look at some research-backed health benefits associated with intermittent fasting to help you decide.
Benefits of Intermittent Fasting
Weight loss. Fasting might be for you if you are overweight or obese and want to lose weight. It’s no surprise that fasting can lead to weight loss, but the evidence has shown that it can be as effective as more traditional diets that prescribe continuous calorie-restriction. A recent literature review described six randomized trials that found short-term fasting to be equivalent to traditional calorie restriction diets, both in regards to weight loss and adherence. Additionally, one of these studies found the fasting group lost more body fat than those following a continuous calorie-restriction diet. The majority of these studies followed a variation of the 5:2 diet (two low-calorie days per week) or an alternate-day, reduced-calorie fast. Studies that provided food on the fast day, as opposed to a zero-calorie day, produced the greatest weight loss.
Reduced heart disease risk. Fasting might be for you if you have elevated cholesterol, triglycerides and/or blood pressure, all of which increase your risk for heart disease. According to the research, fasting may have a beneficial impact on these markers.
A literature review conducted by the American Heart Association found that some small trials of intermittent fasting reduced total cholesterol, bad (LDL) cholesterol and triglycerides. As is frequently the case with nutrition research though, some studies did not find any benefit or came with some caveats. The greatest decreases in triglycerides were generally observed in studies with the greatest weight loss. The same was true for blood pressure — systolic and diastolic blood pressures decreased only in the intermittent fasting studies that achieved a weight loss of six percent or more. The greatest reductions in total and LDL cholesterol were found in participants with mildly elevated cholesterol (i.e., LDL cholesterol >110 mg/dL), which suggests those with higher cholesterol levels may not see as great an impact.
The majority of trials that resulted in significant reductions in total and LDL cholesterol were alternate-day fasts. Both alternate-day fasting and periodic-fasting regimens (i.e., a 5:2 diet) appear to be effective in lowering triglyceride levels, but the effect is dependent on the amount of weight lost. Alternate-day fasting may also be beneficial for lowering blood pressure, but a weight loss of six percent or more may be necessary to see significant reductions.
Reduced diabetes risk. Fasting might be for you if you have elevated fasting blood sugar, elevated fasting insulin or insulin resistance (IR), all of which increase your risk for developing diabetes. The American Heart Association literature review found that intermittent fasting may be effective for decreasing fasting insulin and IR, and reducing fasting glucose in those with prediabetes.
Trials with the largest decrease in insulin had an average daily calorie restriction of 40 percent to 50 percent of baseline needs. For example, in one study participants alternated a day of complete fasting with a day of normal, healthy eating and achieved a 57 percent decrease in fasting insulin. Overall weight loss seems to play a bigger role in reducing insulin resistance, however. The greatest decreases in insulin resistance occurred with the greatest weight loss, but studies show a modest body weight reduction of just four percent can reduce IR in obese individuals.
Fasting might be right for you if you’re overweight or obese and want to lose weight, or if you have some of the markers for heart disease and/or diabetes, including elevated cholesterol or triglycerides, high blood pressure, elevated fasting blood sugar or fasting insulin, or insulin resistance. Of course, fasting is not safe for everyone, so it’s best to consult your doctor before starting any short-term fast, particularly if you’re pregnant, diabetic, underweight or healing from an injury or surgery, or have a serious medical condition.
As for which type of short-term fast is most effective — it’s hard to say given the limited body of research available and the variety of fasting methods used in the relevant studies. History has shown the most effective diets are those you can adhere to long-term, so if you try an intermittent fasting diet, start with the approach that seems most doable and most likely to help you achieve your personal health goals.