Scientists have linked a plant-based diet to a reduction in liver fat
In adults with type 2 diabetes, after 16 weeks of a low-fat vegan diet, body weight and fatty deposits in the liver decreased, and indicators of insulin sensitivity and pancreatic function improved. Participants were not given a daily calorie allowance and were allowed to eat until they were full. However, the study was small and did not include a control group. What does it mean to reduce liver fat by a third, why the composition of a plant—based diet is important, and what conclusions about diabetes treatment are too early to draw - in the Izvestia article.
What kind of diet did the scientists study?
The study tested a specific dietary model: a vegan diet with a low fat content. The diet was based on vegetables, whole grains, legumes and fruits. This model excludes animal products.
Approximately 75% of calories were supposed to come from carbohydrates, 15% from protein and 10% from fat. These fractions describe the contribution of nutrients to the energy value of a meal, rather than their weight on the plate. They also characterize the studied scheme, rather than a universal recommendation for all people with diabetes.
Therefore, the results cannot be automatically transferred to any food labeled "vegan". The exclusion of meat and dairy products does not in itself reproduce the research diet: the products that replace them and the total fat content are important.
For example, a menu of vegetables, beans, and whole grains differs in composition from a diet dominated by sweets and fatty pastries without animal ingredients. Both may correspond to the principle of vegan nutrition, but in the new work we studied the first approach in its field.
What does it mean to reduce liver fat by a third?
During the study, body weight decreased by an average of 6 kg, or 6.6% relative to the baseline. The main part of the decrease was fat mass: it decreased by 4.2 kg. The volume of visceral fat decreased by 290 cc.
The lipid content in liver cells decreased by 33%. This is a relative change in the indicator under study. It does not mean that the liver has become a third smaller or that a third of its mass has been removed from it. Also, we are not talking about reducing the fat content by 33 percentage points.
The distinction is important for understanding the result. The scientists compared the amount of fat in liver cells before and after the intervention and found a noticeable decrease relative to the baseline level. This figure describes the change in body fat, but by itself does not confirm the complete disappearance of liver disease.
The association of this result with diabetes is of practical importance. According to the US National Institute of Diabetes, Digestive and Kidney Diseases, fatty liver disease is common in people with type 2 diabetes, and weight loss with excess can improve liver health.
Why did researchers evaluate the effects of insulin
Insulin is a hormone that helps glucose flow from the blood into cells and be used for energy. With type 2 diabetes, the body responds less well to its effects and may not produce enough insulin. As a result, glucose remains in the blood, and its level rises.
After the dietary intervention, the HOMA-IR index, used to assess insulin resistance, improved. Other calculated indicators — OGIS and PREDIM — indicated an increase in insulin sensitivity.
At the same time, several parameters of the function of beta cells that produce insulin have changed. In particular, the indicators of its release in response to glucose and the sensitivity of these cells to its concentration improved.
This helps explain the interest in the study: favorable changes were noted both in the body's response to insulin and in the indicators of its production. However, such measurements do not prove the restoration of the number of beta cells or the disappearance of diabetes.
How sugar and cholesterol have changed
According to the authors, glycated hemoglobin HbA1c decreased by one percentage point. This analysis reflects the average glucose level over about the previous three months, so it allows you to assess changes in sugar control over a longer period than a single measurement after a meal.
A percentage point and a percentage cannot be substituted for each other here. To clarify, switching HbA1c from 8% to 7% would mean a reduction of one percentage point. This is a conditional example, not the initial and final values of the participants in the new work.
The average decrease itself also does not mean that all patients got the same result or reached the target sugar level. The doctor evaluates the indicators of a particular person, taking into account his condition and treatment.
Total cholesterol and low-density lipoprotein cholesterol, often referred to as "bad" cholesterol, also decreased. In addition, the researchers reported a decrease in the accumulation of AGEs, the end products of glycation. The authors associate these compounds with insulin resistance and damage to beta cells.
However, changes in laboratory and calculated parameters over four months cannot be equated with a proven reduction in the incidence of heart attacks, kidney damage, or other complications of diabetes. Separate, longer studies are required to assess such outcomes.
Why doesn't the lack of calorie counting cancel out their values
One of the features of the work is that participants were not prescribed a specific daily calorie intake and were not required to limit the size of each serving. They were advised to eat until they were full, observing the prescribed composition of the diet.
"For many years, people with diabetes have been told to count calories and measure portions," said Hana Kahleova, lead author of the study and director of clinical Research at the Committee of Physicians for Responsible Medicine.
According to her, the work shows the possibilities of changing the very set of products in favor of vegetables, whole grains, legumes and fruits. Here it is necessary to distinguish between the absence of a set limit and the actual number of calories consumed. A person may not be counting, but after changing the menu they will receive less energy. Therefore, the phrase "lost weight without counting calories" does not mean that the weight loss occurred with the same calorie content.
The study also does not allow us to separate the contribution of weight loss from the contribution of other dietary changes. The participants simultaneously changed the set of foods, the proportion of fat and body weight. To determine which part of the result is related specifically to the exclusion of animal products, specially organized comparisons are needed.
How can this data help you choose your diet?
The new work provides grounds to continue studying such a diet as one of the approaches to nutrition in type 2 diabetes. The changes that affected both body weight, liver fat, and glucose metabolism were particularly interesting.
At the same time, the nutrition plan should take into account the treatment and needs of a particular person. The choice of products, their quantity and the time of reception are important. Vegetables, whole grains, and fiber sources can be included in different healthy diet options.
Refusing to count calories is also not equivalent to refusing to count carbohydrates, if it is necessary to adjust the dose of insulin. Significant dietary changes should be coordinated with the attending specialist, and the dosage of drugs should not be changed independently.
The next step for science is to test the results in larger studies with control groups and long—term follow-up. This will allow us to understand how stable the changes are and which features of the diet make the greatest contribution to diabetes control.
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