The study focused on two versions of the APOA2 gene: C and T. Scientists tested all subjects for which one they had. Additionally, they calculated BMI and collected data on diet by using a survey.
Once they had this data, they looked for a relationship between the APOA2 version and BMI. Nothing obvious showed up. However, when they started to look closely at how fat intake factored in, they found an interesting effect.
They divided the subjects into two groups. One group consisted of people who ate diets high in saturated fats. We'll call this the "high-fat" group. The rest of the subjects were in the low-fat group, having diets low in saturated fats.
In the high-fat group, people who only had the C version had significantly higher BMIs than those with a T version. The result suggests that this gene can affect a person's weight.
However, scientists also had a result that suggested this wasn't strictly true. If BMI is simply based on the APOA2 gene, then people with the C version in the low-fat group would also be heavier. But that wasn't the case.
In the low-fat group, it didn't matter what version of the gene a person had. A person's BMI was pretty much the same whether he or she had the C or T version. So, on a low-fat diet, the APOA2 version doesn't matter. On a high-fat diet, it does.
Of course, there are many things that go into how much a person weighs. For instance, age and gender may make a difference. And there's exercise. What if the T group is more likely to work out and that's what causes lower BMIs?
The average age between the T and C groups was about the same. The male/female ratio was also about the same. As for exercise, when scientists compensate for it, the C group still has a significantly higher BMI than the T group in the high-fat group.
So, what a person eats matters when it comes to weight. And so do genes.
Some genes, like those that affect eye color or baldness, are not really affected by what a person does. Other genes really depend on a person's environment.
For example, height and how likely it is to tear an ACL have been correlated with different genes. A malnourished child may never reach her full height potential and an inactive person may never be in a situation to hurt his ACL. Many traits are the result of what is in a person's DNA and what that person does with it.