We'd all like to eat as much as we want and not gain weight, and a recent study finds that this goal is possible — you just have to eat the right foods. One caveat: This was a study of non-human primates, but the results are likely to apply to human primates as well.

Researchers at Wake Forest School of Medicine looked at the eating behavior of monkeys fed two different diets. Nearly 40 female monkeys were randomly divided into two groups: One group was fed a typical Western diet, high in fat and sugar. The other group of monkeys was fed a Mediterranean diet, rich in fruits, vegetables and whole grains.

The Western diet was formulated to mirror human diets that primarily obtain protein and fat from animal sources, while the Mediterranean diet gets most of its protein and fat from plant foods. Both of the diets fed to the monkeys had similar proportions of carbohydrate, protein and fat. The two groups of animals were similar in baseline weight and body fat at the start of the study.

For 38 months, the equivalent of nine years in humans, the monkeys were allowed to eat as much as they wanted of the diet they were assigned to. The animals fed the Western diet ate all they food they needed and more. As a result, they gained weight and body fat.

The monkeys fed the Mediterranean diet didn’t even eat all the food they were given. They ate fewer calories, and had lower body weight and less body fat than the monkeys that ate the Western diet.

Not only did the Mediterranean diet protect against increases in food consumption and obesity, but it also protected against pre-diabetes and non-alcoholic fatty liver disease, two diseases that are more likely to occur when a person is overweight or obese. About a third of Americans have pre-diabetes. Without changes in diet, weight and physical activity, pre-diabetes can develop into type 2 diabetes.

Obesity is also a major risk factor for non-alcoholic fatty liver disease, which can lead to cirrhosis of the liver and liver cancer, possibly requiring a liver transplant. By 2030, a third of U.S. adults are expected to have the disease.

It's not surprising that a Western diet can be hard to resist. It's designed that way. Red meat, sugary treats and drinks, and fatty foods are key ingredients. “The Western diet was developed and promoted by companies who want us to eat their food, so they make it hyper-palatable, meaning it hits all our buttons so we overconsume. Eating a Mediterranean diet should allow people to enjoy their food and not overeat, which is such a problem in this country,” said principal investigator, Carol A. Shively of Wake Forest School of Medicine, in a statement.

The findings should encourage you to eat healthier foods that you enjoy and quit worrying about food groups or counting calories, fat grams or carbs. The Mediterranean diet is a good guide when it comes to eating as much as you want without gaining weight. Getting started on it is easier than you may think. Focus on eating a variety of fruits, veggies, nuts, legumes and whole grains. Include some olive oil, poultry or fatty fish like salmon. The only foods you need to limit or avoid are red meat, processed foods, and sugary treats and beverages. Pretty easy, isn’t it?

The study is published in Obesity.