Department of Research & Evaluation News

Restaurants in the United States are known for generous portions, often serving far more food than most adults need in a single meal. Those oversized portions have long been linked to overeating and, over time, to higher rates of obesity and chronic disease. A new study conducted in real restaurants suggests there may be a simple solution: serve less food.

Researchers from Kaiser Permanente Southern California partnered with 5 fast‑casual restaurants in Los Angeles County to test whether offering meals under 700 calories would leave diners feeling satisfied. Instead of a laboratory experiment, the analysis took place in two of the five restaurants where people actually eat, order, and socialize. The study was published in March, 2026, in Nutrition and Health.

“This study was sparked by a basic question,” said the study’s lead author, Deborah Cohen, MD, PhD, of the Kaiser Permanente Southern California Department of Research & Evaluation. “If people are served less food in restaurants, will they feel deprived or hungry, or will they feel just as full?”

Dr. Cohen said previous research showed people often eat what is put in front of them without consciously thinking about quantity: “Eating is largely automatic. Portion size is the main culprit for overconsumption.”

To explore this, researchers developed detailed guidelines for what they called “standard portions.” These portions were designed around typical daily calorie needs of about 2,000 to 2,200 calories, with lunch and dinner capped at fewer than 700 calories. Meat was limited to about 3 to 4 ounces, grains such as rice were measured carefully, and vegetables played a larger role on the plate.

The 2 participating restaurants created special menus highlighting these standard portions, labeled “Light and Fresh” at 1 location and “Balanced Portions” at the other. In 1 restaurant, customers ordering a standard portion received a smaller plated meal, while extra food from the regular portion was boxed to take home.

Diners were invited to take part in the study while visiting the restaurants. Participants took photographs of their meals before eating and again when they finished, capturing any leftovers. They also completed a short survey about their age, activity level, height and weight, and how full they felt after the meal using a 7‑point scale. A $25 gift card was offered as an incentive after the photos were reviewed.

In total, 77 people participated, and usable photo data from 63 diners were included in the final analysis. About 2/3 of participants chose a standard portion meal when given the option.

Diners who ordered standard portion meals consumed, on average, about 246 fewer calories than those who ordered from the regular menu after adjusting for demographics. Yet their reported level of fullness was virtually the same as those who ate the larger meals.

Standard portion meals averaged about 482 calories consumed, compared with about 829 calories for regular menu meals. Despite this difference, the average fullness score differed by less than 1/10 of a point on the 7‑point scale.

“What surprised some people is that eating hundreds of fewer calories did not translate into feeling less full,” Dr. Cohen said. She noted that many of the smaller meals included more vegetables, which are lower in energy density but contribute to a feeling of fullness.

The study also found strong customer acceptance: 93% of diners who chose standard portions said they would order them again. More than half took home leftovers, compared with fewer than 1 in 5 diners who ordered regular meals.

For the average person, the findings suggest that bigger portions are not necessary to feel satisfied. Simply being served an appropriately sized meal can naturally reduce calorie intake without requiring willpower or strict dieting. Over time, that difference could help prevent gradual weight gain, Dr. Cohen suggested.

There are limitations. Diners were not randomly assigned to meal types, and the study involved a relatively small number of participants. Still, the researchers say the real‑world setting strengthens the findings.

“There are currently no rules about how much food restaurants can serve,” Dr. Cohen said. “Our study shows that offering standard portions is feasible, acceptable, and could make a meaningful difference for public health.”

In addition to Dr. Cohen, other authors include Magdalena E. Pomichowski, MPH; Vennis Hong, MPH; Jessica Skela, MS; Iris Anne C. Reyes, MPH; Gregg S. Davis, PhD; and Sara Y. Tartof, PhD, all with the Department of Research & Evaluation. Dr. Tartof also is on the faculty of the Kaiser Permanente Bernard J. Tyson School of Medicine.