Scientists Reveal Why Bread Can Cause Weight Gain Without Overeating17 April 2026 ByDavid Nield (Photographer Basak Gurbuz Derman/Moment/Getty Images) New research in mice shows how eating bread can cause body weight and fat mass to increase, even though caloric intake stays at a similar level. The research, led by a team from Osaka Metropolitan University in Japan, highlights how carbohydrates can contribute to weight gain as well as excessive fat intake – which is what dietary advice tends to focus on. This isn't the first time nutritionists have talked about bread and carbohydrates and their contribution to weight gain, but there hasn't been much detailed research into the relationship – especially wheat flour – or into what might be happening at a metabolic level. The team discovered that eating more wheat bread was associated with reduced energy expenditure, pushing the metabolism towards a state where fat storage is prioritized, even when the calories in a diet stay at a similar level. The researchers analyzed the difference that bread in the diets of mice had on their weight (A) and fat tissue (B, C). (Matsumura et al., Mol. Nutr. Food Res., 2026) "These findings suggest that weight gain may not be due to wheat-specific effects, but rather to a strong preference for carbohydrates and the associated metabolic changes," says nutritionist Shigenobu Matsumura of Osaka Metropolitan University. The researchers set up experiments in which lab mice were given a choice between their normal, healthy cereal-based diet and either simple bread, baked wheat flour, or baked rice flour. The mice were then monitored to check their weight and how their bodies burned calories at rest and when active. Using blood samples, the study team also examined hormone, blood sugar, and metabolite levels in the animals, while post-experiment tissue analyses assessed gene expression in the liver. The experiments showed that the mice strongly preferred to switch from their standard diet to carbohydrate-heavy snacks, which then led to weight gain and more fat tissue in the mice, particularly in the males. Further analysis and follow-up tests suggested that these two key changes were being driven not by overeating or a lack of exercise, but by the foods themselves. In the wheat flour diet, fewer calories were being burned overall, while genes responsible for turning carbohydrates into fat were activated. Another follow-up test focusing on the wheat flour group showed that when the chow diet was restored, the weight gain stopped, and the metabolic shifts were reversed. "In the future, we hope this will serve as a scientific foundation for achieving a balance between 'taste' and 'health' in the fields of nutritional guidance, food education, and food development," says Matsumura. The findings are more evidence of how what we eat can cause changes in how our body processes food and burns the calories it contains. In the case of bread, it seems to slow down the body's metabolic engine. One limitation of the study is that it used mouse models, rather than human volunteers. While it's likely that similar processes are happening in people, it's not certain – so that's something future studies can pick up. The researchers also want to experiment with a broader selection of foods to identify what exactly it is about bread that causes this reaction. No diet study like this exists in isolation, of course. We know that a variety of other factors can also impact how our metabolism reacts to food and drink, including age and hormone-related changes. Related: There's a Surprising Link Between a Key Nutrient, Obesity, And Alzheimer's Risk Further research should help establish the role that wheat and bread can play in a diet and how the simple "calories in, calories out" rule isn't always straightforward. "Going forward, we plan to shift our research focus to humans to verify the extent to which the metabolic changes identified in this study apply to actual dietary habits," says Matsumura. "We also intend to investigate how factors such as whole grains, unrefined grains, and foods rich in dietary fiber, as well as their combinations with proteins and fats, food processing methods, and timing of consumption, affect metabolic responses to carbohydrate intake." The research has been published in Molecular Nutrition & Food Research. ARTICLE SOURCE: https://www.sciencealert.com/scientists-reveal-why-bread-can-cause-weight-gain-without-overeating
A low-carb diet is a dietary approach that emphasizes the reduction of carbohydrate intake, particularly from sources such as grains, starchy vegetables, fruits, and sugary foods. The main idea behind a low-carb diet is to reduce the intake of carbohydrates, which are broken down into glucose (sugar) in the body and can lead to fluctuations in blood sugar levels and insulin production. By limiting carbohydrate intake, the body is encouraged to use other sources of energy for fuel, primarily fat, including your own stored fat.
The specific level of carbohydrate restriction can vary, but generally, a low-carb diet involves significantly reducing the intake of foods like bread, pasta, rice, cereal, and sugary snacks. Instead, individuals following a low-carb diet often focus on consuming foods high in protein, healthy fats, and non-starchy vegetables. Examples of foods allowed on a low-carb diet include:
It's important to note that there are variations of low-carb diets. Some common variations of low-carb diets include:
Atkins Diet: Developed by Dr. Robert Atkins, this diet restricts carbohydrate intake, but it has different phases that gradually increase carb intake as you progress through the plan. The initial phase is extremely low in carbs to induce weight loss and ketosis, while later phases reintroduce more carbs while still emphasizing protein and healthy fats.
Low Carb Diet: A general low carb diet aims to keep the total of carbohydrates consumed each day under 100g per day. This closely mirrors the 4th and final phase of the Atkins approach, called the Maintenance plan. Some people on a low carb diet will eat anything as long as they stay under their carbohydrate goals, including processed foods.
Ketogenic Diet (Keto): This is one of the most well-known low-carb diets. It involves drastically reducing carbohydrate intake to a point where the body enters a state of ketosis, usually under 20 actual carbs per day. In ketosis, the body switches from using glucose as its primary energy source to using ketones, which are produced from fat breakdown. Keto dieters aim to eat only fresh, whole, single-ingredient foods that have gone from farm to table, bypassing a manufacturer who may have processed it, with a few exceptions. This means no sugar and no grain in general.
Dirty Keto: This is a hybrid between True Keto and general low carb diets. Those on a "Dirty Keto" diet are usually willing to keep their carbohydrate intake very low, but aren't willing to give up processed food and grains. They bend the rules a bit by counting what is often referred to as "net carbs" instead of actual carbs. Some manufacturers, in order to sell their products, will claim that since certain ingredients they use are low on the glycemic index, or aren't technically sugar, that they shouldn't count the same as regular carbs. While this isn't true, many people still find success by only eating things that are low on the glycemic index.
Carnivore Diet: A dietary approach that consists almost entirely of animal products, to the exclusion of most plant-based foods due to their natural defense chemicals and toxins. It's often thought of as the ultimate ketogenic diet, getting as close to zero carb as possible. Those following a carnivore diet typically consume various types of meat, such as beef, poultry, pork, and fish, but will usually place emphasis on ruminant animals. The diet completely excludes carbohydrates from sources like grains, fruits, vegetables, and legumes.
Ketovore Diet: This dietary approach is a hybrid between a true Keto and carnivore diet. This lifestyle places emphasis on consuming mostly animal-based foods, but isn't opposed to occasional fresh low carb vegetables. The ketovore dieter will usually try to stay under 10 grams of carbs per day during their weight loss journey, but once they have reached their goals some may incorporate fruit into their diet, thus becoming a Paleolithic dieter.
Paleolithic (Paleo) Diet: While not solely a low-carb diet, the Paleo diet emphasizes whole foods and eliminates processed foods, grains, and legumes. This naturally results in a reduced carb intake and places greater emphasis on protein, vegetables, fruits, and healthy fats.
People choose to follow low-carb diets for various reasons, including weight loss, blood sugar control, and to manage or reverse such medical conditions like diabetes, metabolic syndrome, and high blood pressure.
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