Why Am I Gaining Weight When I'm Eating Healthy?

What does "eating well" mean to you? According to one study, 93% of Americans want to eat healthy, and 63% say they try to eat healthy the majority of the time. Seventy-five percent of people rated their own diet as "good, very good, or excellent," yet nearly half of Americans fit the classification as obese! Is America overweight because we don't know enough about what we eat? ("Healthy Eating Statistics," 2023)

In 2019, the National Institute of Health published a study performed on 20 healthy individuals to measure the correlation between processed foods and weight gain. These individuals were admitted as inpatients for one month so their diets could be strictly controlled. For two weeks, half the participants were fed a diet of ultra-processed foods, and the other half were fed a diet of unprocessed foods. After two weeks, the groups' diets were swapped. Significantly, these meals were carefully matched for total calories, total protein, carb, and fat ratios, and total sugar, sodium, and fiber content. In other words, the "nutrition facts" labels would have read almost the same. The "ingredients" list was different, however.

The results of the study found that the groups gained an average of almost two pounds during the two weeks that they ate ultra-processed foods, yet the same people lost an average of almost two pounds during the two weeks that they ate whole foods. This was despite being allowed to ask for "seconds" as much as they wanted (Hoffman, 2019).

While the results of the study might not seem surprising, the actual foods that study participants in the “ultra-processed” group ate might seem quite unexpected. The study authors listed an example meal for lunch and breakfast for the two groups:

Ultra-processed Group - Breakfast

• Bagel

• Cream cheese

• Turkey sausage

Whole-foods Group - Breakfast

• Oatmeal

• Skim milk

• Blueberries

• Raw almonds

Ultra-processed Group - Lunch

• Sandwich on supermarket bread

• Lunch meat

• Cheese

• Baked potato chips

• Diet lemonade

Whole-foods Group - Lunch

• Salmon

• Sweet potato

• Plain yogurt

• Strawberries

According to most Americans’ perception the “ultra-processed” group might actually be considered healthy eating! It wasn’t as though the study participants were fed pizza and hamburgers and sugary drinks.

According to the NOVA classification system, ultra-processed foods are those which include many ingredients, some of which would likely not be found in your kitchen. Unprocessed or minimally processed foods are whole foods such as fruit, vegetables, eggs, milk and meat. It might seem surprising how many of our foods are considered ultra-processed - up to 75% of the average American's diet (Morea, 2021)!

Why did the study participants gain weight when eating foods with the same number of macros? Researchers found that when eating ultra-processed foods, participants were more likely to reach for seconds, and ate at least 500 more calories per day. While this could be presumed to be from simply liking processed foods better, scientists found that the smaller particles of ultra-processed foods actually did not trigger the same hormones to be produced in the gut in response to a meal. Researchers believed that the processed foods actually triggered hunger hormones, whereas the whole foods triggered the normal hormones that tell the body it is full after it eats (Hoffman, 2019).

The important thing to takeaway is that “healthy foods” like yogurt and whole wheat bread may not necessarily be the healthy foods we think of them as, when added sweeteners, preservatives, colorings and flavorings populate their list of ingredients. While this might seem disheartening at first, it’s actually quite enlightening and encouraging to discover one reason why “healthy” eating doesn’t always lead to weight loss.