“Our bodies seem determined to defend the highest body weight possible—both by increasing our desire for food and by decreasing how much energy we burn whenever we experience a calorie deficit.”
– Éric Doucet
In the hit television series Mad Men, overweight housewife Betty Draper struggles to regain the slim figure that had helped her earn modelling contracts and the attention of ex-husband Don Draper. She attends Weight Watchers meetings and diligently limits her caloric intake. In one scene, she carefully measures small blocks of cheese and places them beside her single slice of unbuttered toast and half grapefruit. Later that night, she rushes to the fridge and inhales a mouthful of whipped cream.
Mad Men is set in the 1960s, but Betty’s attempts to lose weight resonate today more than ever. While the multi-billion-dollar diet industry thrives, more than 95 percent of people trying to shed kilos end up relapsing. Losing weight seems an intractable losing battle for most.
Éric Doucet’s research on fasting and dieting may shed some light on why that struggle is so difficult, by exploring how our bodies and brains respond to reduced caloric energy intake. The professor in the Faculty of Health Sciences at the University of Ottawa and his team at the Behavioural and Metabolic Research Unit are studying “food reward”— the amount of work we’re willing to do to procure the food we would like to eat. For the most part, this drive to seek food has been studied in subjects whose weight is stable; Doucet’s team is among the first groups to look at the dynamics of food reward in humans deprived of calories.
“We found that, as we restrict our caloric intake, our desire for food actually increases, likely through a series of mechanisms affecting our dopamine levels,” explains Doucet. “In fact, we’ve seen that a drug like Ritalin, which blocks dopamine reuptake in the brain, decreases food intake and feeding in human subjects.”
His team has also discovered that restricting the energy our body takes in has a big effect on how our food tastes and smells. “If we deprive you of calories, food will actually start to taste better,” says Doucet. “The food experience is enhanced as both taste and olfaction are improved as a result of caloric deprivation.”
This change in taste and smell is possibly modulated by a hormone called leptin. As we lose weight, fat cells release leptin, increasing the intensity of taste, as well as our sense of smell. “This increases the pleasure we experience when eating,” says Doucet. “And if the pleasure of the food experience is heightened, that gets stored in our memory, increasing the motivation to seek food even more.”
Meanwhile, an important gut peptide called ghrelin also plays a key role in appetite by signalling to our brain when it’s time to eat. As we lose weight, ghrelin levels increase, likely diminishing our feeling of being full and driving us to seek and ingest food.
“What’s so surprising and puzzling is just how aggressively our body acts to maintain any weight that we’ve gained,” says Doucet. “And it seems like it’s the change in weight that matters most, much more than actual weight levels.”
The researcher’s team is also looking at how quickly our body burns calories and how that changes during weight loss. The news isn’t good. “When we restrict caloric energy intake, our body goes into a kind of ‘economy’ mode, shutting off everything that is non-essential,” he says. “Our resting metabolism decreases, as does the amount of energy burned after eating. You also burn fewer calories during exercise or any other physical activity.”
Doucet has found that the rate at which this happens is even greater than would be expected from changes in weight alone.
Here’s the problem. Diets are based on how much energy you burn. For example, if you usually expend 2,000 calories a day, you might restrict your intake to 1,500, expecting that you will lose the equivalent of 500 calories a day. But since you’re now running on ‘economy’, you might now be burning only 1,700 calories a day, essentially swallowing up the calorie deficit and therefore losing weight at a much slower rate.
“Our bodies seem determined to defend the highest body weight possible— both by increasing our desire for food and by decreasing how much energy we burn whenever we experience a calorie deficit,” stresses Doucet.
“What’s even scarier is how long these effects last. In fact, data shows that our appetite can be affected by weight loss for as long as a year and energy expenditure for as long as six years,” he adds.
“This is a huge argument for prevention, for avoiding weight gain in the first place. For those who are already overweight, we need to start thinking of weight maintenance, or even the slowing down of weight gain, as success.”
If only Betty Draper knew what Éric Doucet and his researchers now know about the forces at work in the battle of the bulge…
by Leah Geller