After a few more years, the extra 10 pounds can impact a person's health.
Through careful research, scientists have determined which foods lead to weight gain and which lead to weight loss.
The so-called middle-aged spread shows up before most even know it.
"Adults after the age of 30 usually gain about a pound a year. It sneaks up on you," said dietitian Maria Fisk of Providence St. Joseph Medical Center.
The report in the New England Journal of Medicine followed 120,000 men and women for 20 years. Researchers looked at people's diets and determined which foods led to weight gain.
Fisk says it's an eye-opening report.
"It kind of gives people an idea, 'Wow! There's something attached to this food,'" she said.
Eating potato chips can cause about 1.7 pounds in weight gain in four years. Plain potatoes are another 1.28 pounds. Sugary beverages can add another pound. Red meat can cause nearly two extra pounds.
On the other end of the scale, a four-year weight loss was most associated with eating yogurt, nuts, fruits, whole grains and vegetables. People who ate all these foods would lose about 2.5 pounds over four years.
Even for people who include more vegetables, whole grains, fruit and yogurt into their diets, Fisk warns that alone is not enough to lose the weight.
"It's not just switching to (yogurt). Thats not going to do it. It has to be taken in the context of the rest of your life," Fisk said.
Alcohol consumption and poor quality sleep also factored into weight gain.
Researchers calculated 2/5 of a pound for every alcoholic beverage per day. On average, participants gained nearly 17 pounds over the 20-year period. Poor sleep was defined as sleeping less than six hours and more than eight.
People who exercised regularly lost nearly two pounds.