- New research suggests that, particularly for those trying to lose some weight, the old adage that breakfast is the most important meal of the day may be true.
- A small-scale study has found that people with overweight and obesity who followed a diet where they ate 45% of their daily calories for breakfast, and only 20% in the evening, lost weight.
- Effects varied with type of breakfast; those on a high-fiber plan lost slightly more weight and gained gut biodiversity, while those on a high-protein diet reported feeling less hungry, which could help with longer-term weight management.
When you eat, recent research suggests, may be as important for health and weight control, as what you eat, with evidence that eating later in the evening is associated with weight gain.
So should you eat a hearty breakfast instead of a large dinner?
A new study in adults with overweight and obesity suggests this could be advisable. Researchers found that eating a large, protein- or fiber-rich breakfast, and limiting energy intake in the evening was associated with weight loss.
The study, published in the British Journal of Nutrition, found that, while both groups lost weight, those in the protein-rich group experienced less hunger, and the fiber-rich diet led to slightly greater weight loss and an improvement in gut biodiversity.
Thomas M. Holland, MD, physician-scientist and assistant professor at the RUSH Institute for Healthy Aging, RUSH University, College of Health Sciences, who was not involved in this study, told Medical News Today:
“This was a randomized crossover trial, meaning participants served as their own controls, which strengthens internal validity and reduces variability between individuals. The investigators carefully controlled calorie intake relative to resting metabolic rate and measured detailed physiologic outcomes, including thermic effect of food, insulin resistance indices, and microbiome composition.”
“However,“ Holland cautioned, “the cohort was small and predominantly male, and each intervention lasted only 28 days, which limits broader application and long-term interpretation.“
The trial was a follow-on from a
For the new trial, researchers recruited 19 people — two women and 17 men — with a mean age of 57.4 years, and a
They measured participants’ resting energy requirements, then designed eating plans based on these.
For the first 4 days, participants followed their usual diet, then they spent 4 days on a maintenance diet, formulated to provide 1.5 times their resting metabolic requirement.
Researchers then randomly allocated them to one of two big breakfast diet plans for 28 days:
- a high-protein diet — 35% fat, 30% protein and 35% carbohydrate, and no more than 15 grams per day (g/day) of fiber
- or a high-fiber diet — 35% fat, 15% protein and 50% carbohydrate, and at least 30g/day of fiber.
Both diets provided 45% of their calorie intake for breakfast, and 20% for the evening meal. Participants could eat up to 35% of their calories, as desired, at lunchtime.
After 28 days, participants spent 7 days on the maintenance diet, before switching to the other big breakfast plan for a further 28 days.
Participants on both the high-protein and high-fiber plans lost weight during the course of the trial, with those on the high-fiber plan losing slightly more: -4.87 kilograms (kg) versus -3.87 kg.
Both diets also lowered participants’ blood pressure and blood lipids.
Holland cautioned that changes may have been due to the lower-calorie diet, telling MNT: “One important takeaway is that calorie restriction itself drove many of the improvements in weight and metabolic markers. The differences in macronutrient composition shaped appetite signaling, thermogenesis, and microbial metabolite production in meaningful but distinct ways.”
The high-fiber diet increased diversity of the gut microbiome, including increasing the number of butyrate-producing bacteria, which are key to intestinal health and may have other health benefits.
The high-protein diet had the opposite effect, resulting in lower gut microbiome diversity. However, it had the beneficial effect of suppressing appetite, which may help with longer-term weight control.
Alex Johnstone, Phd, PGCE, RNutr, a nutrition scientist at the Rowett Institute, University of Aberdeen, in the United Kingdom, and principal investigator on the study, told MNT that choice of diet would depend on a person’s Health goals.
“Not one diet fits all people. A diet with high protein was good for appetite control and high fiber was good for gut health,” Johnstone said.
“A protein-rich breakfast enhances satiety partly through stimulation of gut hormones such as GLP-1 and PYY that signal fullness to the brain and suppress appetite,” Holland further explained.
“These hormones slow gastric emptying and help reduce subsequent food intake. Protein also has a higher thermic effect of food, meaning more energy is required to digest and metabolize it,” he detailed.
However, according to Holland:
“The limitation is that higher protein intake, particularly if low in fiber, may reduce microbial diversity and decrease production of beneficial short-chain fatty acids. In contrast, a fiber-rich breakfast supplies fermentable substrates that gut bacteria convert into metabolites such as butyrate, which support gut barrier integrity and metabolic signaling. Protein may help someone feel fuller for longer, while fiber works more gradually to support long-term gut and metabolic health.”
Holland explained how energy use varies during the day, noting that “energy metabolism follows circadian rhythms, meaning insulin sensitivity, glucose handling, and diet-induced thermogenesis are generally higher earlier in the day.”
After a meal, he explained that “blood glucose, insulin, and metabolic activity rise in response to food.“
“Earlier calorie consumption may lead to more stable postprandial glucose responses and greater nutrient oxidation rather than storage — the body is more likely to use those calories throughout the day for energy needs, movement, brain function, and metabolic processes, rather than storing them as fat,” he told us.
He called for longer-term trials with larger and more diverse populations to assess sustainability and clinical outcomes beyond proxy biomarkers, adding that “It would also be valuable to examine combined high-protein and high-fiber approaches within early time-restricted eating patterns. The strategy appears promising, but more evidence is needed before universal guidance can be issued.”
Holland further pointed out that “front-loading calories earlier in the day may support metabolic efficiency and appetite regulation for many individuals.“
“However, personalization is critical, as circadian preference, lifestyle, and metabolic health vary,” he cautioned.
Holland recommended that a combination of food types at breakfast might be most beneficial:
“Greek yogurt, eggs, or cottage cheese paired with oats, lentils, chia seeds, or berries provides both high-quality protein and fermentable fibers. […] A breakfast built around a strong protein, plus a variety of plant fibers, and perhaps adding in some fermented foods, may be able to support both appetite control and microbial Health simultaneously.”
