Fasting, whether it’s skipping all food and drink from sunrise to sunset for the month of Ramadan or abstaining from eating meat on Fridays during Lent, has long been viewed by many religions as good for the soul. But is it good for the body as well?

More people today are assuming the answer is yes, thanks in part to the increasing popularity of intermittent fasting, or strategically cycling between periods of eating and periods of avoiding food completely or severely restricting it. The eating pattern comes in many forms. Some people select two days each week to severely limit their caloric intake and allow themselves to eat without restriction the other five days. Others eat only during a certain window of time each day — say, between 10 a.m. and 6 p.m. Others completely fast one or two days each week, limiting their intake to calorie-free beverages for 24 hours at a time.

[See: The DIY Detox: How to Create the Healthiest Cleanse for You.]

The forms of intermittent fasting are endless — and so are the motivations. Proponents’ claims range from weight loss, increased productivity and reduced inflammation to lower risks of heart disease, Alzheimer’s disease and Parkinson’s disease. But are they right? According to an article in the Journal of the Academy of Nutrition and Dietetics that reviewed all available research (at the time) on intermittent fasting, few of these claims are supported by long-term research, and those that are came as a result of animal trials. More specifically, the article concluded:

— Studies on rodents support the idea that limiting feeding to normal nighttime hours improves metabolic profiles and reduces the risk of obesity and obesity-related conditions.

— It appears that almost any intermittent fasting plan can result in some weight loss. After all, it’s likely that by limiting when and how much you eat, you’ll also reduce your total caloric intake enough to result in weight loss.

— Plans that involve fasting every other day appear to result in weight loss and reductions in glucose and insulin concentrations. That said, only three studies have been done on the topic and the researchers warn that the extreme hunger experienced with this type of plan may make it impractical and unsustainable.

— Research has not demonstrated that alternate-day fasting programs produce greater weight loss than standard weight-loss plans.

— There is plenty of rodent-based data on the positive effects of time-restricted eating, but limited data from human studies.

— There are little or no published data linking intermittent fasting with clinical outcomes such as a reduced risk of diabetes, cardiovascular disease, cancer or other chronic diseases.

While this article didn’t articulate any dangers of intermittent fasting, other studies have shown that fasting (in rats) led to increased blood glucose that could lead to cell damage and, even more alarming, stiffness in heart tissue that impeded the organ’s ability to effectively pump blood. What’s more, many weight-loss experts warn that intermittent fasting may lead to substantial overeating of unhealthy, high-fat foods during non-fasting periods, ultimately undermining followers’ efforts.

[See: 7 Diet Mistakes Sabotaging Your Weight Loss.]

As a health and fitness professional, I’m also concerned with how intermittent fasting may negatively affect people’s ability to reap the benefits of exercise. Food is fuel, and that fuel is necessary to drive movement, whether you’re hitting the hiking trails or lifting kettle bells in the gym. So, what happens when you fail to provide fuel for long stretches of time?

Under normal circumstances, the body uses stored carbohydrates to fuel exercise. When those stores are depleted, the body searches for other energy sources and will turn to both fat and protein stores. Many proponents of intermittent fasting cite the fact that the body burns more fat during exercise than during a fast, but they fail to mention that the body will be burning — and losing — more muscle as well.

It’s also important to note that burning protein will not only adversely affect your muscular strength, but it will also slow your metabolism, making weight loss more difficult in the long run. Science has shown that building muscle through resistance training is an essential element of both sustained weight loss and overall health; fasting makes that much more difficult.

Many proponents of intermittent fasting recommend that you perform low-intensity cardio workouts on fasting days and save high-intensity cardio and resistance-training workouts for days when you’re eating normally. If you choose to fast, this approach makes some sense. Still, it’s far from ideal or recommended.

Intermittent fasting, no matter what form it takes, represents a dramatic overhaul in the way a person eats. Such changes should only be done after careful consideration and research. It’s best to talk to your doctor before starting any kind of fasting plan.

[See: 8 Food Trends Nutrition Experts Pray Will Never Return.]

If you decide to try intermittent fasting as a means to achieve weight loss or any other health-related goal, do your research and find the form that best suits your individual lifestyle. As with any changes to your diet or overall lifestyle, trying to force the issue through sheer willpower will rarely yield lasting positive results.

More from U.S. News

How to Make Healthful Dietary Changes Last a Lifetime

5 Extreme Diets You Shouldn’t Try

9 Ways to Actually Make Eating Well Fun This Summer

What Are the Potential Risks of Intermittent Fasting? originally appeared on usnews.com