Weight fluctuates. Some seasons (ahem, winter) the scale goes up. Diets and workout routines can bring it back down, but it's not at all uncommon for the weight to rebound. According to 2007 research from the University of California, Los Angeles, about two-thirds of people who lose weight gain it all back — and then some — within five years. These fluctuations have become common, but they're anything but healthy.
"When your weight fluctuates, you are blowing up your body with molecular changes," says Michael Snyder, Ph.D., director of genomics and personalized medicine at Stanford University School of Medicine. His 2018 study published in Cell Symptoms identifies 318 separate genes that work differently when people gain as little as six pounds (or even less). Some turn on, others turn off and some may never return to normal, he says. Here experts explain five side effects of weight fluctuations.
1. Slower Metabolism
When you lose weight, your basal metabolic rate — the number of calories your burn performing everyday functions — decreases, says Alexandra Sowa, M.D., a diplomate of the American Board of Obesity Medicine. "For every 10 percent of body weight lost, a person needs to consume 20 percent fewer calories to maintain that weight," she says.
This is partly due to a loss in muscle (it's rare to lose 100 percent fat and 0 percent muscle when you drop the pounds) as well as genetic and hormonal changes. Meanwhile, hunger-regulating hormones — including ghrelin, leptin, peptide YY and insulin — get out of whack.
"People who have experienced multiple bouts of weight loss and regain commonly have higher levels of hunger during their lowest weight, but, unfortunately, their level of hunger even remains higher when they have regained the weight," says Jeffrey Sicat, M.D., an Obesity Medicine Association board of trustees member.
When you gain weight, the vast majority of genetic changes occur in the genes related to your immune system and regulation of inflammation, says genomicist Dr. Michael Snyder. And a 2009 study found that by damaging the body's DNA, chronic inflammation plays a critical role in the development of medical conditions like cancer, autoimmune disorders and cardiovascular disease. It may also drive overeating and weight gain, per 2017 Cell Metabolism research. Talk about a vicious cycle!
In a 2018 University of Oxford study of 10,428 women, those who weight cycled (science speak for yo-yoing) over a 12-year period were significantly more likely to suffer from depression. While the study only determined that there is a link between weight cycling and depression — not that one causes the other — research from 2014 published in PLOS ONE also found that a person's risk of depression increases after successfully losing weight.
Experts aren't yet sure exactly how weight fluctuations impact mental health, but inflammation, low levels of lean muscle mass and chronic diseases like diabetes and cardiovascular disease are linked to depressive symptoms, says Dr. Jeffrey Sicat.
4. Heart Disease
Modest weight gain triggers changes in genes related to cardiomyopathy (diseases of the heart muscle), says genomicist Dr. Michael Snyder. "This is weight gain not unlike what you might see over a winter holiday," he says. "And some of the effects are longer lasting."
He notes in his recent Cell Symptoms study that small gains in weight triggered changes in fatty-acid metabolism (how the body breaks down fat for energy). Those changes stuck around even after people lost the weight they had gained.
That may partly explain the finding that people who experience weight fluctuations of 8.6 pounds have double the risk of suffering a heart attack, stroke or death when compared with those who fluctuate by less than two pounds, according to a 2017 study published in the New England Journal of Medicine.
5. Insulin Resistance
The previously mentioned 2017 study from the New England Journal of Medicine also found that the larger your weight fluctuations, the greater your risk of developing Type 2 diabetes in the future. If you're wondering what the possible connection could be, genomicist Dr. Michael Snyder says that in his research, even a small weight gain resulted in changes to the microbiome — the trillions of bacteria, viruses and fungi that call the human body home. "These changes inhibit metabolic control and may pave the way for insulin resistance, prediabetes and diabetes," he says.
How to Avoid Weight Fluctuations
By now you may be thinking: "I've lost and regained the same five, 10 or 15 pounds over and over again in my life. Have I totally screwed up my body?" So let's take a beat here and realize that there are so many things that can negatively affect your body — smoking, alcohol consumption, a sedentary lifestyle — but no one thing spells imminent disease or death.
Weight fluctuations are common, but the best thing you can do to keep yourself healthy is to avoid crash diets or anything that causes extreme weight gain or loss. Find a weight that's realistic for your body and lifestyle and maintain a healthy and consistent diet to keep your weight in check.