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
Wanted to start a dedicated thread on this, as I am still learning, and have more questions than answers, but a bit of experience to bring to the table. Sorry in advance if this gets long.
I am two years in on the carnivore diet, and (to my knowledge) properly fat adapted. I can consume fats with relative abandon with no restroom related "side effects" shall we say.
As a type1 diabetic, I can definitely spend a good portion of anyone's time singing the praises of what I have been informed is something called gluconeogenesis, as it keeps me from having to carry sweet snacks always at the ready. I can work along, and not worry about low blood glucose most of the time, even as a type1. I have proven to myself that a zero carb diet is the way to health, especially with type1 in the mix, but I dont wish this thread to be isolated to those with a specific knowledge of diabetic physiology. As an additional thought, wearing a CGM (continuous glucose monitor) allows me to get a different perspective on what is happening as my body processes different foods and situations. Its my hope that some of this may be a help to others (as well as yours truly!)
Many folks here speak about being kicked out of ketosis if they consume carbs or sugars, and while I notice this myself, I ALSO notice that if I eat anything that contains sugar or carbohydrates, it will seemingly hamper my gluconeogenesis abilities, and I will drop terribly low in the hours following the compromised meal. This is as opposed to the normal days where I have eaten "clean" and my glucose level will drop to say, 70 and then self correct and I can go right on working (or sleeping) like its nothing.
I have been trying to get a straight story from all my internet searches (heh, get in line, right?!) ...so wanted to poll the community here for everyone's thoughts.
In another thread (that I didnt want to hijack) Bob spoke about "adaptive glucose sparing" and some of it's effects.
Here are my observations, please critique, or add to these with your thoughts!
- When I have been able to keep my diet SPOTLESSLY clean for many days in a row (no cheats, ever) my sugar levels seem to stay right on target and I feel simply amazing! I have been under the assumption that me being properly fat adapted, I am in these times reaping the benefits of adaptive glucose sparing.
Something that I am beginning to suspect, is that adaptive glucose sparing is akin to ketosis in that a dietary change can "kick us out" for a while. Is this at all correct?
I further notice that *sometimes * when I fast for any longer than one meal, my glucose levels can sometimes rise and stay elevated as if I just ate an oreo cookie! This happened most recently at a dr visit, and I was amazed at how high my glucose level was (145) even though I had not eaten anything for nearly 24 hours! ( @Geezy has made a comment in a recent post suggesting that I may have fasted too long before the appointment, which can throw your numbers off?) Anyway, I say *sometimes, because it doesnt seem to be a hard and fast rule, and on other occasions I can go for days and not have my sugar level rise at ALL, even with fasting!
There are also many regular days when no fasting is going on, and my diet has been a proper balance of meats and fats, but I throw some cheese in, I notice that after my midday meal, my sugar level goes up considerably as if I was back on the cookies again! Ill be sitting there later on thinking to myself "what the heck did I EAT??!!" as my blood sugar level is going up past 175! I have so far attributed this discrepancy to diet (perhaps as a result of eating things like cheese maybe?) and that in these times I am experiencing gluconeogenesis without the benefit of adaptive glucose sparing? Am I on the right track here?
Is the cheese (or even a small amount of dairy) enough to shut down adaptive glucose sparing to the point that my body begins creating a sizeable amount of glucose from the protein I just ate? Does it work like this? It certainly seems like it, but these are the questions I have in my head day to day.
Lastly, I hear just a bit about a process from time to time called glycogenolysis, that is similar to gluconeogenesis, but is instead the body's conversion of glycogen to glucose.
Is glycogenolysis actually what is saving me during the times I would drop "low"?
According to the internet at large, a high fat diet increases insulin resistance, but I have experienced my insulin resistance going DOWN as a result of carnivore, as well as my A1C.
Okay, Im done for a minute. Please let me know your thoughts!