If you’ve made a New Year’s resolution to eat right and trim down, be forewarned that medical science shows your brain has it in for you and will actively promote your failure on two different fronts. That’s not good news, of course, but you should know about it so you can strengthen your resolve as best you can.

Here’s the scoop. It’s relatively easy — particularly if you are significantly overweight — to lose a few pounds by reducing the number of calories you consume each day.

The problem is that your initial success will trigger a couple of responses in your body. First, as you lose weight a hormone called leptin — which is produced by your fat cells — will start to drop in concentration. That change tells your brain that your stores of fat are decreasing. The brain responds to that report as if famine is on the way. The body makes changes to conserve its energies, and your metabolism will drop.

Metabolism — the rate at which we burn energy — is a major key to what our weight tends to be. Your metabolism may differ from that of John or Jane. But it also will change compared to what it was before you lost weight. The lower your metabolism, the easier it is to consume more calories than you burn in a day — triggering weight gain.

Here’s how that works in practice. Imagine you weighed 175 pounds for a number of years, but then your weight creeps up to 200 pounds. You go on a diet and successfully get back to 175. Congrats! But your metabolism is likely to now be slower at 175 than it would have been if you’d always weighed in at that one amount. In other words, science has shown you have to eat fewer calories to maintain yourself at 175 pounds than you would have if you had always weighed that amount.

What this means is that, depending on your weight loss, you may face a 300 to 500 calorie “handicap.” To beat that handicap you’ll have to eat that many fewer calories each day to maintain yourself at your new weight compared to someone who had never been overweight.

But the scientific news gets worse.

At your post-diet weight of 175, there’s a double whammy. Simply put, you’ll likely feel plenty hungry after your weight loss. The reason is that some other brain chemicals will be triggered that tell you that you feel peckish. In short, your appetite will be stimulated by the fact that you’ve lost weight. So on the one hand you’ll need fewer calories than someone of your weight who has never dieted, while at the same time you’ll feel hungrier than someone who has always been slim and trim.

What’s a poor person sincerely trying to be faithful to a New Year’s resolution to do?

For one thing, the experts agree it’s pointless to try fad diets like eating only dill pickles. The best chance of success you have is to modify your diet toward eating right in a way you can do for the rest of your natural life. “Dieting” shouldn’t be about short-term weight loss based on serious deprivation — you need to find what works for you that you can sustain over the long term.

Another key to success is exercise — and yet more exercise after that. General medical advice is to get 30 minutes per day of moderate exercise. But to maintain weight loss, you’ll likely have to do better. Many advisors in medical science say a person needs to do an hour of exercise each day to keep off pounds shed through dieting.

Nothing about weight management is easy, and scientists are learning more and more about how and why it’s so difficult to lose weight and keep it off.

But if you’re like me, January is a good time to make some changes — changes you can stick with throughout all the weeks and months of this bright and shiny New Year. Others have done it successfully in the past — so let’s encourage one another to take on the serious but rewarding work of helping our health through diet and exercise.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Follow her on the web at rockdoc.wsu.edu and on Twitter @RockDocWSU. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.