If you’re worried about overeating and its consequences you’re not alone. Half the people surveyed by WW (formerly Weight Watchers) said they’re eating more due to the pandemic, and in a WebMD poll nearly half of the women said they gained weight. Surveys aside, the WiFi connected scale company Withins analyzed the aggregated data from more than 2 million users under self-isolation and found that the average weight gain was only 0.21 pound — about 3 ounces.
Maintaining body weight is tough in the best of circumstances. People usually slowly gain weight over time; Americans gain an average 1–2 pounds a year. Our situation nowadays is quite unique though, as so many of us are undergoing a dramatic change — that’s why it’s been dubbed the quarantine 15, similar to the shift in weight students are rumored to undergo when they first move to college.
When life’s disrupted eating patterns change.
The Freshman 15 might be a bit of an exaggeration. But are we experiencing a worldwide experiment in caloric overload? And if so, are we indeed going to see a big jump in overweight and obesity? Or is our body’s tendency for keeping weight around a setpoint going to kick in and somehow make the extra energy, or the overeating itself, sort itself out?
The science of overeating
The biology of human overfeeding has been studied since the early 20th century. A recent article in Obesity Reviews looks at 70 years of research and more than 300 scientific papers on the subject.
The first few studies, which took place before 1950, studied just one volunteer — the researcher himself — and reported less weight gain than expected, suggesting the body “wastes” some of the extra energy away.
Later studies gathered sophistication and volunteer numbers, some were short term, lasting just a few days, some lasting as long as 6 months, utilizing many overfeeding regimens.
Analyzing this data holds both reassurance and warnings.
There’s a wide variability between people’s response to overfeeding. Focusing on studies in which people were overfed an overall 50,000 kcal extra, people gained from 7 to 17 pounds, and the difference between people equally overfed was as much as threefold. There’s clearly a genetic component, twin studies show. Age, gender and ethnicity seem to matter, and some of the most important predictors are baseline fat-free mass and fitness — muscular, fit people gained less weight. People with a family history of diabetes and insulin resistance are at higher risk of weight gain when they overeat.
Do we waste energy when overfed?
Overall, although the excess amount of calories correlates with weight gain across 19 studies relevant to this issue, people gain less weight than expected. The old rule of thumb is that every extra or deficient 3500 calories result in one pound of weight gained or lost, but in overfeeding studies only 60 percent of calories translate into accumulated fat, and weight gain isn’t linear, it slows over time.
Some of this extra energy may be wasted through a rise in resting energy expenditure — overfeeding can increase metabolic rate. Studies also show that during overfeeding the energy cost of physical activities, such as walking, climbing stairs etc. goes up. Some animals, such as rodents, dissipate extra energy as heat when they’re overfed, but we humans usually don’t have the talent to activate brown fat in this way.
Does the kind of food you overeat matter?
This relates to a longtime debate in nutrition: Is a calorie just a calorie, or does the source and quality of the food affect weight outcomes? While it’s clear that certain foods lend themselves to overeating — an open pack of Oreos can quickly disappear, yet an equal calorie huge bowl of broccoli rarely does — experiments in which overeating is imposed show that what you eat affects fat storage location.
Overfeeding on a low protein diet increases the percentage of energy stored as fat. Fat type also makes a difference: Adding more saturated fat as opposed to polyunsaturated fats leads to increased fat accumulation in the abdomen and in the liver.
Several studies compared overfeeding high carb and high fat diets. Blood insulin, fatty acids and other biomarkers changed according to the diets; weight gain, however, was similar. An interesting study compared overfeeding with candy to overfeeding with peanuts for two weeks. Equal amounts of consumed calories led to almost 2 pounds of weight gain, and an increase in waist circumference when eating candy, and just about half a pound in the peanut group.
But overall, the authors conclude that the overfeeding diet type plays a big role in fat distribution but not a significant one in the amount of fat stored. Fat distribution is pretty important though.
What happens when overfeeding ends?
When participants completed overfeeding studies, they lost the gained weight rapidly within a few weeks or months, even if they weren’t trying to. Just returning to the pre-overfeeding diet, without intentional caloric restriction, led to recovering the pre-overfeeding weight status.
This has been documented in many studies.
With this, too, there was wide interpersonal variability.
Stay calm and nourished
These stressful times call for kindness to yourself, so if you feel like you’ve strayed a bit try not to worry, but rather, correct course when you’re able.
Research shows again and again that it’s the long term habits that matter, and just like short periods of overindulgence during the holidays don’t matter so much, baking your way through Covid-19 doesn’t mean you’re on a slippery slope towards unbridled weight gain.
This large-scale review offers a bit of reassurance: Overfeeding affects people less than they fear, and bouncing back from it may require less effort than anticipated.
And here’s another thought: When life’s disrupted eating patterns change. That’s why now’s a golden opportunity to change them for the better.