People often generalize and oversimplify metabolism, but it’s actually an extremely complex process. As a quick refresher, metabolism relates to how your body produces energy from fat, protein, and sugar/carbohydrates and how it stores that energy. You’ve probably heard people say they have a slow or fast metabolism, but what they’re actually referring to is their metabolic rate: how much energy/calories they burn in a day.

Strength training and eating more protein and healthy fats are expert-approved ways to improve (aka speed up) your metabolic rate. To find out if eating patterns such as intermittent fasting improve or slow down your metabolic rate, POPSUGAR spoke to Avigdor Arad, PhD, RDN, CDE, director of the Mount Sinai PhysioLab.
What Is Intermittent Fasting?
Simply put, intermittent fasting (IF) is a type of eating pattern in which you eat and fast within specific time windows. There are a variety of ways to do IF, with 12:12 (you eat within a 12-hour window and fast for 12 hours) and 16:8 (eating in an eight-hour window and fasting the other 16) being two of the most popular methods. Unlike other ways of eating, you don’t have to restrict what you consume when following IF.
Does Intermittent Fasting Affect Your Metabolism?
“Fasting is so interesting, because if you really think about it from an evolutionary perspective, fasting was always part of our life,” Dr. Arad told POPSUGAR. He explained that because of this, the body has different mechanisms that allow it to handle fasting particularly well. Whether or not fasting is healthy is up for debate, he explained, noting that some studies suggest that fasting could improve your metabolism, your insulin sensitivity, and “different markers that relate to longevity and to health and wellness.”

According to Dr. Arad, your body typically goes into fasting mode after eight to 12 hours, but this depends on how much glucose you have in your blood and how long it takes to deplete the sugar stored in your liver. Once your body hits fasting mode, “it’s trying to conserve the little amount of sugar that we have, and it’s really trying to rely on fat,” he explained.
What Happens to Your Hormones When You Fast?
As your body shifts to burning fat as its main source of energy, Dr. Arad explained that your insulin levels are very low. Conversely, “hormones like adiponectin (which regulates sugar and fat metabolism) and growth hormone and epinephrine (commonly referred to as adrenaline) are very high,” he said.

Because your insulin levels are low, “our blood vessels expand so there is more flow of nutrients and oxygen to the blood or to the working muscle or to the organs in general. And there are all those different hormones that are increasing just to mobilize fat to provide for energy,” Dr. Arad explained.

Dr. Arad said researchers don’t know too much about adiponectin yet and explained “it affects the cells’ ability to take in sugar and fat and use it for energy, and it affects how and where we store fat.” According to Dr. Arad, “Adiponectin levels are affected by lifestyle, namely bodyweight, nutrition, and exercise.” He further explained that low adiponectin levels are associated with weight gain, and weight loss is one of the best ways to increase your adiponectin levels.

“All of those hormonal changes that involve, or are associated with, fasting seem to be healthy,” said Dr. Arad. Although it isn’t definitive as to whether fasting will greatly improve your metabolic rate, some research has shown that it may improve your metabolic rate.

If you’re still undecided about beginning intermittent fasting and want to improve your metabolic rate, Dr. Arad said that as long as you follow a healthy diet, don’t eat too much, and eat real food, you can reap the health benefits — fasting or not. “On the contrary, people who fast, and do it smartly, can certainly gain a lot of benefits.” According to Dr. Arad, “There are a lot of positive effects associated with fasting, as long as it’s done very wisely.”

Be sure to consult your primary care physician before making any changes to your diet.