When I was still overweight, I used every excuse in the book.
It's my genes.
I can't help it.
I've tried, and nothing works.
My body's just meant to be fat.
It's all crap. I was failing because I wasn't doing the things I needed to do. I was dieting, but not holding myself accountable, so I still overate. I was exercising, but also not enough and without making significant changes to my diet. Despite wanting to lose weight, I wasn't serious enough to stay on top of it.
Don't get me wrong. I hated being fat. I hated seeing myself in photos. I hated trying on clothes. However, lifestyle changes are hard, and it's so easy to make up excuses that do you little good.
While I was in the middle of losing weight, I got into an argument without someone who claimed that it was nearly impossible for an overweight person to successfully lose weight and that I was an exception.
It's only improbable because it is difficult to make dramatic lifestyle changes. For me to do it required holding myself accountable for how much I ate, and making a point to get exercise most days of the week. I rarely allow myself excuses or allowances for breaking away from my healthy habits, and that is the key. Yes, I will have to do this for the rest of my life. Oh noes! If you do not take care of your body, your health will fail that much sooner. A healthy diet and active lifestyle is still important even if you're not trying to lose weight.
However, I take offense at being dismissed. I don't think I'm the exception, and I don't think anyone actually wants to feel helpless and trapped in a situation.
This person even argued that some people could eat 1200 calories a day and gain weight because their bodies are just too efficient at using energy. I responded by saying that sounds like the perfect triathlete to me. If you can make a calorie go further, there's no reason not to do endurance-based activities. I did not get a response to that argument.
Today, though, I think you can start to throw out the "I can't help it cause it's in my genes" argument.
Summary: researchers were study men with prostate cancer. The men, rather than go for conventional treatment, underwent some major lifestyle changes including filling theirs diets with fruits, vegetables, whole grains, legumes, and soy products; exercising 30 minutes a day; and spending an hour a day on stress management (meditation, etc.). They saw improvements in their health, but more importantly, the researchers saw changes in their genes (some genes became active and others became inactive).
I don't think genes alone make most people overweight, though, genes affect things like fat storage and possibly things related to how you build muscles and how well you absorb things from food. Genes and environment play the largest factors in obesity. Your genes you apparently can do a few things about. Your environment, you can do a lot about you. You have control over you. You control what you eat and how much. You can choose to be active or sedentary at any given moment. You are not helpless.