Intermittent fasting continues to be a popular approach to weight loss and overall health. But does it work, and is it good for your heart? 

While the jury is still out as to whether it can shed pounds faster than traditional dieting, some studies point to potentially significant heart benefits by lowering rates of heart failure and contributing to a longer life span.

“Unfortunately, research studies on intermittent fasting have been limited, making it difficult to determine whether it works better than other diets and if the heart benefits found in these studies are accurate,” says Tori Nawojski, MD, RD, LMNT, Nebraska Medicine registered dietitian.

What is intermittent fasting?

Intermittent fasting involves alternating periods of not eating or significant calorie reduction with periods of normal eating. The goal is to increase the amount of time your body is in a fasted state. Fasting has been shown to increase metabolism.

Some of the most common methods include the 5:2 diet, in which a person eats normally for five days each week, and then restricts food intake to 500 to 600 calories on two nonconsecutive days. 

Two other popular variations include the 16:8 and 14:10 methods. With these plans, dieters fast for 16 hours or 14 hours and then eat normally for 8 or 10 hours. 

“The bottom line, to lose weight, you have to achieve a calorie deficit,” says Nawojski. “Therefore, you have to expend more calories than you take in. Diets in general can be helpful because they make you more mindful about what you’re eating. But they can also be hard to maintain, and what works for one person may not work for someone else. So whatever diet you can be most consistent with is what I generally recommend.” 

Is intermittent fasting good or bad for the heart?

The most significant research involves a 2019 study published in the AHAIASA Journal. Researchers followed approximately 2,000 people who had undergone cardiac catheterization for an average of 4.4 years. The study found that participants who had been fasting regularly for at least five years had a 45% lower mortality rate than those who did not fast. 

Using the same patient data, another study found that routine fasters had a 71% lower rate of developing heart failure than non-fasters.

“The question is whether the results of these studies would translate to a much larger and general population,” says Nawojski. 

Will intermittent fasting reap greater results than traditional dieting?

A study published in the July 1, 2017 issue of JAMA Internal Medicine involved 100 overweight people over one year. Participants were divided into three eating plans: a daily calorie-restricted diet, alternate-day fasting or no dietary changes. 

At the end of the study, both diet groups had lost weight compared with those who continued their usual eating habits. While the fasting group had lost a few more pounds, it was not statistically significant. The fasting group also experienced a high dropout rate of 38%.

“While intermittent fasting can be a good thing for some people, there are some potential pitfalls due to human nature and biology,” says Nawojski.

Potential drawbacks of intermittent fasting:

• It may be difficult to maintain long-term, leading some people to cheat or stop following the plan. 
• There may be temptation to indulge in unhealthy food on non-fasting days. 
• A biological urge to overeat following fasting days due to increased appetite hormones that can surge after fasting.

Other potential benefits of intermittent fasting:

In addition to weight loss and the potential heart benefits found in the 2019 AHAIASA Journal study, additional research performed primarily on animal models point to other benefits that may be experienced by the body in a fasted state.

These benefits may include:

• Reduction of cellular growth pathways and increased cellular repair and recycling mechanisms as metabolism changes its main source of fuel from glucose to ketones.
• Increased insulin sensitivity, antioxidant defenses and mitochondrial function, which is essential to produce energy.
• Lower rates of diabetes, high cholesterol, high blood pressure and obesity as a result of reduced insulin resistance and inflammation.
• Reduction of heart disease risk by improving blood sugars, blood pressure, cholesterol, triglycerides and body weight.

Who should avoid intermittent fasting?

If you are considering intermittent fasting, always discuss it with your doctor first, says Nawojski. 

Certain people who should not try intermittent fasting, include:

• People with Type 1 diabetes.
• People who take medications for high blood pressure or other heart disease conditions.
• People with eating disorders.
• Pregnant or breastfeeding women.
• People who have a procedure or surgery planned in the near future. 

“Anyone who adopts a healthier diet with fewer calories is going to lose weight,” says Nawojski. “And with any diet, you need to be consistent in eating well-balanced meals and incorporating exercise to maintain long-term results.”