With weight gain, slow and steady is the common pace—we often look back, wondering: “How did I get to this weight?” Long-term weight gain typically happens at a miniscule 1-2 pounds per year, which can snowball into something substantial as we age. Fad diets lure us with the promise of rapid weight loss, but researchers are looking at it from a different angle: Can changing what we eat stop long-term steady weight gain?

What the Science Says

Scientists from the Friedman School of Nutrition Science and Policy did a study using data collected from 120,784 healthy, non-obese, middle-age participants in three well-established cohorts: Nurses’ Health Study, Nurses’ Health Study II, Health Professionals’ Follow-up Study. Data was collected at every four-year period for 16 to 24 years.

Researchers were interested in how participants’ diet quality affected their trend in weight gain. Without altering anyone’s food intake, the researchers looked at what participants consumed, with a focus on protein and the glycemic load (GL)—two measures of diet quality. Then, they examined how changes in participants’ weight corresponded to diet quality. Why?

High-protein foods (think meats, dairy, nuts, beans) are thought to help with weight loss because of their ability to promote satiety, spare lean muscle mass, and help offset the slow in metabolism. GL was used because it reveals both carbohydrate quality and quantity. The more popular “glycemic index” (GI) is used to assess how a food will increase your blood sugar, but this doesn’t account for the amount of the food that you eat. GL accounts for both the food’s GI and portion eaten. High GL foods (think refined carbs) are thought to make weight gain more likely because they make your blood sugar rise rapidly—leading to insulin release, which favors fat storage.

Weighty Findings

Once the data was collected, the researchers could then summarize “associations,” also known as data trends, between certain types of food and weight gain or loss. Here are some of their weightier findings:

• Not all protein foods are created equal. Certain protein foods appeared to be better than others when it comes to preventing weight gain. Nuts, peanut butter, fish, yogurt and low-fat cheese were associated with weight loss while red meat and processed meat were associated with weight gain.
• Eggs and cheese aren’t necessarily diet-busters. These foods were only associated with weight gain if the diet’s glycemic load was also high.
• High glycemic load diets were worse for weight loss. Foods with a high glycemic load (think white bread, potatoes, soda) were associated with weight gain. A diet with a higher GL ranking is positively associated with weight gain. In fact, a 50-unit increase in daily glycemic load (about two bagels) resulted in a 1-pound weight gain every 4 years.
• The type of protein consumed worked in combination with GL to affect weight. For example, someone who eats a high glycemic load diet plus a lot of red/processed meat would gain more weight than if he ate a low glycemic load diet with the same amount of red/processed meat.

Keep in mind that the results of this study are “associations” meant to show relationships between diet quality and weight gain or loss. This does not confirm that particular diet types cause weight gain or loss. Nonetheless, these relationships are still important, given that we’re looking at a large group of participants over the course of decades.

What’s the Takeaway?

This study confirms that the quality of your diet matters for keeping your weight in check over a long period of time. A balanced diet rich in whole grains, fruits and vegetables will help you maintain a low glycemic load. Choosing lean protein sources like chicken, fish, nut butter and low-fat cheese will reduce the amount of fat—particularly saturated fat—in your diet. Both glycemic load and protein type are indicators of your diet quality, and will affect your weight.

It’s apparent that a calorie is not a calorie in this case, so do calories still count when it comes to weight loss? The answer is a resounding Yes! Even though the study focused on diet quality, this is just one factor out of many that affect our weight. To be successful at maintaining a healthy weight, both the number of calories consumed and the quality of those calories matters.

Author Trinh Le is a dietitian consultant for MyFitnessPal. She holds her master’s in public health, nutrition from the University of North Carolina, Chapel Hill, and is a registered dietitian.