Reduced Adipose Tissue Inflammation May Ensue from Pursuing a Vegetarian Diet

Implanting the View that a Plant-based Diet Reduces Adipose Tissue Inflammation

The world is becoming vegan-friendly as a greater number of individuals have started adopting a vegetarian/vegan diet. Ironically, the shift is seen prominently in non-vegetarians who have started following a vegetarian diet owing to several personal reasons whereas, increasing number of vegetarians are turning out to be chicken, meat and fish lovers. Call it open-mindedness, an interest to explore different cuisines or simply the urge to do something forbidden, this transition wasn’t expected! As we see vegetarian, semi-vegetarian and even the stricter vegan diet that excludes even dairy and eggs apart from meat and fish becoming popular their nutritive quality and the ability to satisfy nutrient requirements have always been questioned. People adopt a vegan/vegetarian diet owing to different reasons and the most famous of all is health. These people believe that avoiding consumption of animal products helps prevent the risk of bacterial and other foodborne diseases and also avoid excess intake of saturated fat cholesterol and sodium. There are some who believe a plant-based diet to be rich in nutrients, phytochemicals, fiber and flavonoids, some who don’t eat due to their opposed view on the slaughter of animals for food and others who don’t eat simply due to religious beliefs.
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Vegetarian diets are rich in fruits, vegetables, whole grains, legumes, nuts, seeds and soy foods and their characteristics have maximum benefits on the heart, have been associated for a long time with reduced blood pressure rates, reduced inflammation and have also decrease the risk of diabetes, cancer, renal diseases, rheumatoid arthritis and even obesity. Obesity has always been linked to various co-morbidities but the underlying mechanism for these isn’t clear. We have data linking adipose tissue inflammation and chronic diseases associated with obesity. Adipose tissue macrophages (ATMs), especially pro-inflammatory macrophages (M1 ATMs) are linked with insulin resistance. What remains a mystery is whether the accumulation of ATMs in human beings is only related to fat gain or whether it is related to diet also. Ceramides, a family of lipid molecules composed of sphingosine and a fatty acid, is found in high concentration within cell membrane of cells and has often been linked to inflammation and insulin resistance in muscle cell models. Increased exposure to saturated fatty acids shows increase in ceramide levels in rodents and these molecules have also been linked to adverse muscle profiles in humans. In such a scenario, researchers wanted to know whether pursuing a vegetarian diet would benefit the obese individual such that he/she would have less adipose inflammation and reduced muscle ceramide content in comparison to similar obese individuals who follow a non-vegetarian diet.

The adipose tissue is a complex organ that comprises of a variety of cell types with diverse energy stores, metabolic regulation and neuroendocrine and immune functions. When obesity strikes, the adipose tissue succumbs to disorders, its function and distribution is affected and also has effects on cytokine, lipid storage and composition of adipose-resident immune cell population causing advanced consequences on inflammation and insulin sensitivity. Earlier studies detected lipid composition differences of adipose tissue in rats which were fed a diet rich in polyunsaturated fatty acids (PUFAs). Linolenic acid is the major PUFA present in human adipose tissue and allows estimation of the stored essential fatty acid. The fatty acid composition of the adipose tissue is closely connected to the dietary fat content and studies show that individuals on a long-term vegan diet display increased composition of PUFAs and reduced levels of saturated fatty acids compared to omnivores and even vegetarians.
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Study on whether A Vegetarian Diet Leads to Less Adipose Inflammation
The study included 16 participants among which 8 of them were vegetarians and 8 were omnivores. All the participants were of the same age and BMI without any chronic conditions such as diabetes or cardiovascular disease. All the vegetarian participants assured following a vegetarian/vegan diet for at least last 5 years and among these 8 participants 2 of them were vegans, one was a lacto-ovo vegetarian, one was a pescatarian and four were lacto-vegetarians. Blood samples were taken, a food frequency questionnaire was given and subcutaneous abdominal and femoral adipose tissue biopsies were collected using a needle liposuction technique. Muscle biopsies were also collected and tested for sphingolipids concentration. Plasma total free fatty acid (FFA) concentrations were measured and plasma IL-6 and TNF concentrations were measured. Fat cell size was measured and composition of fatty acids in tissue lipids were also assessed by extracting tissue lipids. For immunohistochemistry (IHC), adipose tissue samples were taken and viewed under a microscope. Two observers took 10 random images of the slide and counted the number of positively stained macrophages, crown-like structures (CLS) and total adipocytes for each image. Resulting data was expressed in terms of number of positive cells per 100 adipocytes. RNA samples were isolated from abdominal and femoral adipose samples for all omnivores and 5 of 8 vegetarians and analyzed.

Results
Both the groups did not differ greatly with respect to age, BMI, body composition or blood pressure. Fasting plasma insulin concentrations, plasma IL-6 and TNF concentrations did not differ between the 5 omnivores and vegetarians taken for sampling. The answers in the FFQ helped researchers to confirm that vegetarians adhered to a plant-based diet and also could find out no significant difference in macronutrient and micronutrient intake among vegetarian subtypes. Total calorie intake showed not much of a difference between the two groups; total saturated fat intake was lesser in the vegetarian group but there was no difference found in the case of monounsaturated and polyunsaturated fat intake between the two groups. Individuals following an omnivorous diet consumed more of cholesterol and vitamin D while vegetarians ate more of fiber and vitamin C.

Vegetarians had more of oleate in the abdominal depot than omnivores and also had more of oleic, palmitelaidic, linolenic and myristic fatty acids in the femoral depot. Plasma FFA palmitate occupied a lesser percent of total FFA in vegetarians compared to omnivores while other fatty acids did not show any significant difference. Both the groups did not show any difference in the abdominal or femoral adipose tissue depot macrophage burden and the number of abdominal adipose tissue macrophages was also not different when expressed per 100 adipocytes. Vegetarians had fewer femoral CD68 and CD14 macrophages compared to omnivores. Omnivores had more CD206 macrophages in femoral fat than vegetarians. Adipose tissue TNF mRNA expression was greater in omnivores than vegetarians but there was no significant difference in femoral adipose tissue expression of either TNF mRNA or IL-6 mRNA between the two groups.

There was no difference seen in muscle ceramide concentrations between the two groups nor any significant correlation found between adipose tissue macrophage burden and intake of total calories, total fat, saturated fat or polyunsaturated fat. Trans-fat and added sugars intake were correlated with total macrophage burden and there was a positive correlation between abdominal CD206 macrophage and monounsaturated fat intake and omega-3 fatty acid intake. The study clearly shows that individuals following a vegetarian diet for at least 5 years consume less saturated fat and is also linked with reduced femoral adipose tissue inflammation.

For all those of you who have been struggling to succeed with a switch over from your favorite non-vegetarian diet to a vegetarian diet, this article would definitely be a motivating factor to continue your endeavor as it is not only good for health, helps in weight loss and reduces the risk of diseases but also helps in sustainable living.

References
Preliminary Evidence for Reduced Adipose Tissue Inflammation in Vegetarians Compared with Omnivores: https://nutritionj.biomedcentral.com/articles/10.1186/s12937-019-0470-2

In Vivo NMR, Applications, Other Nuclei: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/adipose-tissue