Lean Times

Here are some weighty facts: In Canada, half of the provinces will have more overweight adults than those of normal weight by 2019; worldwide, the prevalence of obesity has more than doubled since 1980, rapidly advancing in unexpected places like China, India and North Africa.

And now it seems staying slim and trim is harder than ever. York University researchers have discovered that those with the same calorie intake and physical activity levels had an average body mass index of 2.3 kilograms per square metre higher in 2006 than in 1988.

The study, conducted by Professor Jennifer Kuk in York’s School of Kinesiology & Health Science, and her colleague Ruth Brown, lead researcher and York graduate student, analyzed dietary data of nearly 36,400 American adults collected by the National Health & Nutrition Survey between 1971 and 2008. The available physical activity frequency data of 14,419 adults in the 1988 to 2006 period was also used.

Although the average food and energy intake around the world has increased over the past few decades, it’s not the only reason for weight gain. The belief  that weight gain is simply the result of people consuming more calories than they burn is now being questioned by researchers.

Weight management is much more complex than simply “energy in” versus “energy out,” says Kuk, the study’s senior author.

“Saying the above is true is similar to saying your investment account balance is simply your deposits subtracting your withdrawals, and not accounting for all the other things that affect your balance – like stock market fluctuations, bank fees or currency exchange rates,” she says.

“Our study results suggest that if you are 40 years old now, you’d have to eat even less and exercise more than if you were a 40-year-old in 1971 to prevent gaining weight. However, it also indicates there may be other specific changes contributing to the rise in obesity beyond just diet and exercise.”

If you are 40 years old now, you’d have to eat even less and exercise more than if you were a 40-year-old in 1971 to prevent ­gaining weight

The York study reports that people consuming a given number of calories were 10 per cent heavier in 2008 than in 1971, and about five per cent heavier for a given amount of physical activity in 2006 than in 1988.

“These secular changes may in part explain why we have seen the dramatic rise in obesity,” says Brown.

Kuk says our body weight is affected by our lifestyle and environment, including medication use, genetics, timing of food intake, stress, gut bacteria and even nighttime light exposure.

In an article in a recent issue of The Atlantic about her research findings, Kuk proffers that people today are exposed to more chemicals that might increase weight gain. She suggests that pesticides, flame retardants and even substances found in food packaging could be altering our hormonal processes and, in turn, the ways our bodies gain and maintain weight.

Second, she mentions the use of prescription drugs has risen dramatically since the 1970s and ’80s, some of which have been linked to weight gain.

Finally, Kuk and other experts think the gut microbiomes of North Americans may have changed between the 1980s and now. It’s now known that some types of bacteria can make a person more prone to weight gain and obesity, she says. Antibiotics may also be affecting our gut bacteria in subtle ways.

We are also eating more meat than we were a few decades ago and much of that meat is likely treated with hormones, which promote growth. Kuk believes artificial sweeteners may be playing a role in our weight gain, too.

What does all this add up to? Kuk says, for a start, we need to move away from weight bias – that is, simplistically judging people who are obese as being lazy and self-indulgent.

“There are many factors in our modern society that make maintaining a lean body weight more difficult, even with a proper diet and regular exercise. Nevertheless, having a good diet and regular exercise is still important for achieving the best health at whatever body weight.”