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Why Your Holiday Feast Won't Make You Fat

Hannah Martin Lawrenz

During short-term bouts of overeating, regular exercise can guard against pudge-promoting inflammation and altered fat metabolism. Learn more...

From tightened belts to post-dinner naps, we’ve all experienced the effects of overeating during the holidays—followed by guilty trips to the gym. Now, encouraging research from the University of Michigan shows how regular aerobic exercise can protect our bodies from a week of excess calories.

Previously, scientists estimated that even short-term overeating could cause expansion of fat tissue and impaired metabolism. In fact, earlier studies linked a week of overeating to impaired glycemic control and insulin sensitivity. Although some researchers thought exercise could protect against these problems, few actually studied the effects of regular exercise on fat tissue before and after short-term overeating—something most of us experience on vacation and during the holidays.

“Right now, actually, research in fat is sparser than research in muscle and some other tissues in the context of diabetes,” said lead researcher Alison Ludzki. “We want to be able to better understand the timeline of certain changes that happen in fat, like in overeating.”

Ludzki’s curiosity prompted her to enlist colleagues in analyzing what happens when active adults completed a week of overeating alongside regular aerobic exercise.

The team recruited 4 lean, active adults to consume 30% more than their daily energy requirements for 1 week. At the same time, participants maintained their regular exercise habits (over 2.5 hours of planned aerobic exercise across at least 6 days of the week). The researchers measured participants’ oral glucose tolerance and took abdominal fat samples before and after this overeating test.

After the week of feasting, participants gained a pound or two and did not show impaired glucose tolerance, echoing established research findings. Surprisingly, however, overeating also did not cause increased fat tissue inflammation or lipolysis.

“Previous examinations have found increased inflammation in fat and circulation from a few weeks of overeating, so we thought we would see the same in 1 week,” explained Ludzki. With more total fat and calories consumed during overeating, the team also expected more lipolytic flux overall, as well as more fatty acids in adipose tissue and released into the circulation (one of the leading theories of how excess nutrition causes insulin resistance in peripheral tissues such as muscle).

“I think it is important to consider short-term overeating independent from the effects of long-term overeating and of obesity,” explained Ludzki. “None of our subjects were obese, so these results tell us what’s happening with people who are of normal weight or overweight who overeat but don’t yet have type 2 diabetes, allowing us to evaluate some earlier changes.”

Next, Ludzki’s team intends to analyze the effects of longer-term overeating (i.e., for more than 1 week) and how they relate to exercise. Many of the changes they have found so far prompt structural alterations over time but not immediately after 1 week. Applications of this research could further support the value of exercise in maintaining metabolic health and may prompt researchers to measure fat function regularly as a variable in addition to muscle function.

“There is definitely a paucity of data from studies that assess the dynamic changes in adipose tissue expansion and function during interventions such as exercise,” noted adipose tissue biologist Ursula White at Louisiana State University’s Pennington Biomedical Research Center, who was not involved in this research. This pilot study provides convincing novel preliminary data that set the stage for future studies to examine how exercise affects the metabolism of specific tissues, which has not been characterized.”


Ludzki AC, Gillen JB, Guth LM, et al. “Effects of Exercise on Adipose Tissue Responses to Short-Term Overeating in Healthy Adults.” APS Intersociety Meeting: The Integrative Biology of Exercise. Hyatt Regency, Phoenix, AZ. 2016. Presentation.

Keywords:  metabolism fat exercise diet