Some people remain thin no matter what. Although others drive themselves crazy by following the latest fad diet and work out with a near obsession for losing weight, these people can eat all they want and hardly pay attention to exercise. A number even wish to put on some extra pounds, but try as they might, they just can’t.

An American doctor is hoping that his recently concluded study may provide clues as to why certain individuals find themselves on the lighter side of the bathroom scales. Daniel Bessesen, chief endocrinologist at the Denver Health Medical Center, related that he and his team started following 60 people since 2003 to measure indicators like weight and to monitor their regular diet and energy expenditure.

The subjects were divided into two categories: those who were naturally thin and others who were prone to becoming fat or obese. They were also overfed in intervals by as much as 40 percent from their normal food intake to see how their bodies reacted, according to Bessesen, who is also a professor of medicine at the University of Colorado.

“I came into this with a strong bias that a lot of weight was determined biologically,” Bessesen told the Georgia Straight in a phone interview. His team is still analyzing the results of the study, but he said that in some cases the environment seemed to have played a role in some weight changes.

Bessesen cited as example the case of one woman who gained 15 pounds over the years. He said that this seemed to have happened after she changed jobs following an ankle injury and then got married.

However, Bessesen noted that there was at least one pattern that emerged from the study, for which results have yet to be published. “We found that there was no difference in physical activity when the two groups are on an energy-balance diet, but following overfeeding, the obesity-prone people tended to move a little bit less and the obesity-resistant people tended to move a little bit more, such that there was a significant difference,” he said. “That may be one of the ways that they don’t gain weight.”

Four years ago, Bessesen coauthored a research report that looked into the short-term effects of overfeeding on hunger, feeling of satiety, and energy intake. For this particular study, the authors recruited “healthy individuals” with ages ranging from 25 to 45. Using body-mass index—the ratio of height to weight—as a measure, they divided their subjects into thin and reduced-obese individuals, meaning the latter were made to lose eight to 10 percent of their initial weight before the study started.

According to the report, the thin people felt less hunger by dinner time right on the first day of the overfeeding.

“Overfeeding resulted in a significant reduction in pre-meal hunger ratings in the thin individuals while no change was seen in the RO [reduced-obese] individuals,” the report stated.

This reduction was more prevalent among thin women, who reported that they felt less hunger across all meals, while the overfeeding effect was “only apparent” for thin men during dinner.

“Interestingly, mean pre-breakfast hunger ratings actually increased during overfeeding in the RO women,” the study noted.

The report also pointed to a “significant increase in mean post-meal satiety ratings in both groups during overfeeding, yet there was a significantly greater increase in the thin individuals”.

There were no significant differences between the two groups with respect to their food intake after the overfeeding cycle, the study also noted.

“In conclusion, these findings demonstrate that three days of 50-percent overfeeding results in appropriate changes in hunger and satiety in thin individuals who are resistant to weight gain and obesity,” the study stated. “On the other hand, RO individuals who are at high risk for weight gain and obesity do not appropriately respond to three days of 50-percent overfeeding.”

UBC medical professor Laird Birmingham is the former director of the eating-disorders program at St. Paul’s Hospital’s and a recognized expert in issues relating to human weight issues.

In an interview with the Straight, Birmingham pointed to the concept of non-exercise activity thermogenesis—or NEAT, for short—as a possible explanation why some are naturally thin. He explained that NEAT refers to the amount of calories people burn off with activity other than exercise. He noted that it could result from something as ordinary as twiddling one’s thumb or chewing gum.

“People who are very thin have a higher NEAT,” Birmingham said. “If you want to look at it the other way around, people who are obese have a much lower one. An average obese person has a 375-calorie a day lower NEAT.”

Birmingham also said that he’s used to seeing people who seek his advice on how to put on weight because they feel bad about being thin.

“If I conclude that they have a constitutionally low body fat, I explain that that is the normal weight for them, and if they tried to change this it wouldn’t be good for them,” he said. “There’s a variety of weights and heights and lengths of hair and everything in the world.”

Birmingham claimed that most people have a stable weight and an “even more stable body fat” throughout their lifetimes. He noted that the “coefficient of variation of body fat” for most is 0.3 percent.

He emphasized that trying to gain weight by simply eating too much could pose dangers. “If you are a male and you’re in your 40s and 50s and your belt size goes up two notches, it does not matter what it [previous weight] was,” Birmingham said. “Your risk of heart disease may be increasing.”

As SFU’s chief strength and conditioning coach, Derek Hansen trains athletes and is also involved in nutrition counselling.

Hansen pointed out that just like others, the athletes he works with come in different body makeup, from muscular ones to those who are thin and to others who “tend to be more obese”.

“It depends on what social setting you’re in,” Hansen told the Straight. “If you’re in a football team, it’s [being thin] not very good. If you’re a Lance Armstrong, having a very thin upper body is actually good for your sport.”