It’s tough for millennials these days. They hate being in the presence of other millennials, they are struggling to find jobs, and they’re buried under unhealthy debt. They are also surpassing Baby Boomers as the largest age group in the United States, meaning we’re only going to hear more about their problems. Here’s something: According to a new report from York University, millennials may have to eat less and exercise more to keep obesity away.

Researchers from York University’s Faculty of Health found that parents of millennials could eat more and exercise less than their kids, all while still avoiding obesity. “Our study results suggest that if you are 25, you’d have to eat even less and exercise more than those [who are] older to prevent gaining weight,” said Professor Jennifer Kuk, of the School of Kinesiology and Health Science, in a press release. “However, it also indicates there may be other specific changes contributing to the rise in obesity beyond just diet and exercise.”

The study analyzed the dietary data of more than 36,000 American adults who participated in the National Health and Nutrition Survey between 1971 and 2008. The researchers also used data that told how often 14,400 of the adults were physically active between 1988 and 2006.

“We observe that for a given amount of self-reported food intake, people will be about 10 percent heavier in 2008 than in 1971, and about five percent heavier for a given amount of physical activity level in 1988 than 2006,” noted lead researcher Ruth Brown, a York University graduate student. She went on to say that these changes may be why obesity is so much more prevalent today than it was in 1971.

As you may know, once you achieve your weight loss goals it can be difficult to turn your diet into a long-term lifestyle. Kuk explained that this is because “weight management is actually much more complex than just ‘energy in’ versus ‘energy out.’” She equated it to a person’s bank account balance. It’s not just that money goes in and comes out when you need it; you need to account for factors that affect your money, like “stock market fluctuations, bank fees, or currency exchange rates.”

She went on to say that “maintaining a healthy body weight is now more challenging than ever.” Factors like our lifestyle and environment; the medications we take; our genetics, and stress all affect our body in different ways, and contribute to our weight in small but important ways.

Source: Kuk, J, et al. Secular differences in the association between caloric intake, macronutrient intake, and physical activity with obesity. Obesity Research & Clinical Practice. 2015.