4. You don't like to exercise (it could be in your genes).
According to Daniel Pomp, PhD, from the University of North Carolina at Chapel Hill, animal research suggests that 25%-50% of an individual's propensity for voluntary exercise is under genetic control.
Pomp studies mice that genetically prefer to exercise because they were bred for high levels of wheel running. Expect more research in the next few years on "exercise genes" and how they might also be at play in humans.
5. Your mother ate a high-fat diet while pregnant.
There is some preliminary research in primates that suggests eating a healthy, moderate-fat diet is important for the future weight and health status of the developing fetus, regardless of whether the pregnant mother was obese or lean.
6. What you ate as a toddler could be affecting how easily you gain weight as an adult.
Research from Raylene Reimer, PhD, RD, a researcher from the University of Calgary, has indicated that the food we eat affects how active certain genes are in our body. "In particular, we believe that our diet has a direct influence on the genes that control how our bodies store and use nutrients," explains Reimer.
In Reimer's research with rats, a group that ate a high-protein diet when young packed on much more weight and body fat as adults compared to another group of rats raised on a high-fiber diet.
More research needs to be done to understand the mechanisms at work here, but this research suggests how complex weight gain really is.
Can't Lose Weight? Focus on Health
If several of these reasons apply to you, don't get discouraged. You can't change your genes, but you can change how you interact with your environment. The positive way to proceed is to eat and exercise for the health of it. Eating mostly healthy foods, avoiding overeating, and exercising regularly is important for your overall health.
And don't beat yourself up if you can't fit into that pair of skinny jeans. The truth is that people naturally come in all sorts of shapes and sizes, says Joanne Ikeda, MA, RD, nutritionist emeritus of the University of California Berkeley nutrition science department, who has spent her career researching weight and health.
"It's so sad that we are convinced that the normal range of human body sizes and shapes should fit into a narrow spectrum when size diversity is, in fact, what naturally occurs in the human population," Ikeda says.