Lose Weight Without Reducing "Food Intake"? Why a Low-Fat Vegan Diet Reduced 357kcal Per Day

When starting a diet, many people first think about "reducing the amount they eat."

Halve the rice. Stop snacking. Lighten dinner. Enter daily calorie intake into an app.

The idea that you need to control energy intake to lose weight is not surprising. However, the problem is how to achieve it.

Reducing food intake can easily lead to hunger. Prolonged hunger can cause stress, making it difficult to continue for a long time.

This is why the idea of "not reducing the amount you eat, but eating the same amount while lowering the overall calorie content of meals" is gaining attention.

A study published in the medical journal "JAMA Network Open" in August 2026 showed intriguing results regarding this approach.

Participants who adopted a low-fat vegan diet showed a significant reduction in energy intake of about 357kcal per day compared to the control group, despite not having a significant decrease in the weight of the food they ate.

The reason the research team focused on was "energy density."

16-Week Trial Involving 244 Participants

This study reanalyzed data from a randomized controlled trial conducted in Washington D.C., USA, from 2017 to 2019.

Out of 3,115 people screened by phone, 244 overweight adults who met the criteria participated in the trial.

Participants were randomly divided into two groups of 122 each: one adopting a low-fat vegan diet and the other continuing their usual diet as a control group.

The vegan group primarily consumed fruits, vegetables, grains, and legumes.

Notably, researchers did not set an upper limit on calorie intake, such as "1,500kcal per day or less."

There were also no clear restrictions on the amount of food consumed.

The method, known technically as "ad libitum," allows eating as needed.

However, after 16 weeks, despite no statistically significant reduction in the total weight of food consumed, there was a clear difference in energy intake.

Although energy intake decreased in both groups, the reduction was greater in the vegan group, with a difference of about 357kcal per day between the groups.

It's important to note what is meant by the expression "the amount eaten did not decrease."

This does not mean "calorie intake did not decrease."

What did not change significantly in the study was the "weight" of the food consumed.

In other words, while eating the same weight of food, the calories contained within were reduced.

The Key is "Energy Density"

Energy density explains this mechanism.

Energy density is a figure that indicates how many kcal are contained per gram of food.

For example, oil contains a lot of energy even in small amounts.

Conversely, vegetables and some fruits have high water content, so even if you eat a considerable weight, the calories do not become very high.

There are foods that provide only a few dozen kcal per 100 grams, while others can provide several hundred kcal for the same 100 grams.

Thus, even if the plate size and food weight are the same, the combination of foods can create a significant difference in total calories.

In this study, the energy density of the low-fat vegan group's diet decreased by about 30%.

No significant change was observed in the control group.

The research team's analysis linked the removal of animal-based foods like meat and dairy from the diet and the increase in low-energy-density plant-based foods like vegetables and legumes to this change.

In other words, they lowered the calories per bite without reducing the "bulk" of the meal.

"Eating Less" and "Eating More Low-Calorie Foods" Are Different

In traditional diets,

the method of "halving your usual meal"

is often used.

On the other hand, the method of lowering energy density involves

"replacing the food on your plate with lower energy density options."

This becomes the concept.

Even with the same 500 grams of food, the total calories can differ between a high-fat, high-energy-density dish and one that includes more vegetables, beans, and grains.

This difference is also important when considering the sustainability of a diet.

People do not eat just numbers like calories.

In reality, satisfaction is gained through seeing the dish on the plate, chewing, swallowing, and the feeling of food in the stomach.

Therefore, simply reducing the quantity can lead to the problem of "not feeling satisfied even after eating."

Low-energy-density foods can potentially keep energy intake low while ensuring a certain volume.

The point of this study is not to say "calories are not important."

Quite the opposite.

It is believed that the reduction in calorie intake led to weight loss.

However, the possibility was shown that calorie reduction could be facilitated by the composition of foods, rather than relying solely on "willpower to endure eating less."

Lower Energy Density Tends to Lead to Greater Weight Loss

The research team also analyzed the changes in energy density and weight change among participants.

The results showed that participants with a greater decrease in energy density tended to experience more significant weight loss.

Furthermore, this relationship remained even after statistically adjusting for changes in energy intake.

In the original randomized controlled trial from 2020, which served as the basis for this analysis, the low-fat vegan group lost an average of 5.9 kilograms over 16 weeks.

The same study reported changes in metabolic indicators such as insulin sensitivity.

The 2026 study is better understood as a re-examination of the mechanisms behind previously observed weight loss from the perspective of energy density, rather than conducting a new weight loss trial.

"Just Being Vegan" Doesn't Explain It All

It's important not to misunderstand that

"you'll lose weight no matter what you eat as long as it's vegan."

This is not the conclusion.

Even plant-based foods can be high in calories if they contain a lot of oil, sugar-laden sweets, or snacks.

Nuts, while nutritious, have high energy per weight.

The study focused on a "low-fat vegan diet," not just any "vegan diet."

The focus was on a diet centered around fruits, vegetables, grains, and legumes.

Therefore, it cannot be interpreted as "stopping meat and dairy and eating a lot of vegan sweets or fried foods will yield the same results."

What might be applicable to general eating habits from this study is the idea of "increasing low-energy-density foods in meals," rather than becoming a complete vegan.

Criticism on Social Media: "This Isn't New"

When the study was introduced on social media and online communities, the reactions were not entirely one-sided.

In Reddit's science news community, there were opinions questioning the novelty of the study.

Since there have been previous studies showing that eating more low-energy-density foods and a diet high in plant-based foods lead to weight loss, there was criticism that it was merely confirming what has been shown many times before.

Indeed, the concept of energy density itself is not new.

The research paper also cites past studies showing that low-energy-density diets affect energy intake and satiety.

In that sense, the mechanism that "plant-based foods have a lot of water and dietary fiber, making it easier to keep calories low relative to meal volume" was not suddenly discovered in 2026.

On the Other Hand, Some Say "Not Having to Manage Quantity Was Important"

In contrast, another user pointed out that the point of this study was not "discovering for the first time that a vegan diet leads to weight loss."

The important aspect is that participants did not have to meticulously calculate calories or reduce the amount they ate, yet energy intake decreased as a result.

Regarding low-calorie diets,

"Won't you be hungry all the time?"

"Won't you need to eat a lot to feel satisfied?"

are common concerns.

However, in this data, the weight of the food consumed did not significantly decrease.

This point was evaluated as "interesting because it differs from simple dietary restriction."

Additionally, there were posts from users who had experienced being vegetarian or vegan, reflecting on how they might have been on a high-fat vegan diet, leading to frequent hunger and increased cooking and eating occasions.

Some people are considering the research results in relation to their own eating habits.

"16 Weeks Doesn't Tell Us About Long-Term Success" - Cautious Opinions

One particularly important point raised on social media was the issue of "whether it can be sustained long-term."

While 16 weeks is a certain period for dietary intervention research, weight management needs to be considered over several years.

Even if a significant change in diet can be made in the short term, whether it can be sustained for years is another matter.

On Reddit, while the effect of energy density was appreciated, with the food weight being almost the same, there were opinions expressing a desire to know if the same effect could be maintained long-term.

Another user expressed skepticism, noting that while there are many ways to lose weight in the short term, the important question is whether weight loss can be maintained in the long term.

This is an important perspective when reading this study.

The study lasted 16 weeks and did not prove that "continuing this method for five years will result in the same pace of weight loss."

Focus on the "Low-Fat" Condition

On social media, there were reactions suggesting that the "low-fat" aspect might be more important than "vegan."

This is reasonable for understanding the study.

Since fat has high calories per gram, lowering the fat ratio in meals tends to work in the direction of lowering energy density.

Therefore, explaining the results solely as "losing weight because meat wasn't consumed" is too simplistic.

Multiple changes occurred simultaneously, such as replacing animal-based foods with plant-based ones, increasing foods high in water and dietary fiber, and adopting a low-fat diet.

The research team also highlighted the increase in low-energy-density plant-based foods like vegetables and legumes as an important change.

The Study Has Its Limitations

While the results are intriguing, it cannot be concluded that "this solves the diet problem."

First, this study is a secondary analysis using existing randomized controlled trial data.

While the researchers showed that those with decreased dietary energy density experienced greater weight loss, this analysis alone cannot definitively attribute all weight loss to energy density.

Another important point is that self-reported dietary records were used to understand meal content.

Participants recorded a three-day food diary at the start and at 16 weeks, which was used for analysis.

There can be errors in dietary records, such as recording less than what was actually consumed or forgetting to record altogether.

The researchers themselves acknowledged this as a limitation.

Additionally, participants were volunteers who voluntarily joined the study, and the same results may not apply to everyone.

In the original trial, the average age of participants was about 54 years, and about 87% were women.

Whether similar results would occur in people of different genders, ages, living environments, and cultural eating habits needs to be examined separately.

Funding Sources Should Also Be Checked

When reviewing a study, it's important to look at funding sources and author affiliations, not just the results.

The 2026 paper was funded by the Physicians Committee for Responsible Medicine, which conducts research and educational activities focusing on plant-based nutrition.

Several authors are also affiliated with this organization.

The paper's conflict of interest section discloses consulting fees related to statistical analysis and positions held by authors within the organization.

However, the paper states that the funders did not participate in the study design, data collection, analysis, manuscript preparation, or decision to submit the paper.

Having funding does not automatically make research results correct or incorrect.

It's important to evaluate the research methods and results, including such information