Maneka Sanjay Gandhi

To understand how plant-based diets can affect your health, you have to understand how the bacteria in your intestine or gut works. The gut “microbiome” is the totality of microorganisms, bacteria, viruses, protozoa, and fungi  present in the gastrointestinal tract.

The gut harbours the greatest density of microorganisms in the body (up to 1.5 kg of bacteria), with Firmicutes, Bacteriodetes and Actinobacteria constituting the dominant category of bacteria.

Bacteroidetes are the largest in number and are divided into Bacteroides and Prevotella.

The Human Microbiome Project is a scientific research project which is trying to measure health by looking at the bacteria in the gut. What are the different bacteria in each individual’s intestines, and are they created by the diet? In a sample of 98 individuals, Wu et al. found that a diet high in protein and animal fats created more Bacteroides, whereas a diet high in carbohydrates was associated with more Prevotella bacteria. In simple language: Prevotella is associated with plant-rich diets which have high levels of complex carbohydrates, fruits and vegetables, whereas Bacteroides is linked to a high intake of fat and protein found in meat.

The Prevotella to Bacteroides ratio (P/B) has been shown to be involved in the success of dietary interventions targeting weight loss. If the Prevotella bacteria are greater than the Bacteroides, the weight loss is higher compared to low P/B. Simply put: vegetarians/vegans are likely to lose weight faster than meat eaters. Recent studies also show that the saliva of meateaters is different to the saliva of vegans.

A study done by M Kim, Hwang et al "Strict Vegetarian diet improves the risk factors associated with metabolic diseases by modulating gut microbiota and reducing intestinal inflammation", found these changes in the  gut when they put 6 obese patients on a vegan diet for a month: Less pathobionts which are  potentially disease-causing organisms, more protective bacterial species and an improving lipid (fat) metabolism - which means fats were being broken down for energy and for constructing cell membranes. Since the majority of lipids found in the human body from ingesting food are  triglycerides and cholesterol, this means that less were found. Also shown was a reduced level of intestinal inflammation. The authors showed lower counts of Bacteroides, Bifidobacterium (which comes from dairy), E. coli and Enterobacteriaceae compared to omnivores. Enterobacteriaceae is a large family that includes Escherichia coli, Klebsiella, Salmonella, Shigella and Yersinia pestis. Enterobacter species are responsible for causing urinary tract infections (UTI), respiratory infections, soft tissue infections, osteomyelitis, and endocarditis, among many others.

The Bacteroides organisms are potential problems for human health. If they escape the gut,  they can cause significant disease including abscess formation in multiple body sites (e.g., the abdomen, brain, liver, pelvis, and lungs), as well as bacteremia or the presence of bacteria in the blood.

Prevotella are neither good nor bad: neutrality is their motto and they cannot cause disease. These bacteria break down tough fibres, like xylan and hemicellulose, that are found in plants.

The authors showed that a change in diet to high-fat/low-fibre, or to low-fat/high-fibre, changed the microbiome in one day, and this change could last upto ten days.

In a 30-day study, David et al. found that fermentation processes linked to fat and carbohydrate decomposition were much better if there was an abundance of certain microbial species like Prevotella. They found a strong correlation between fibre intake and Prevotella abundance in the microbial gut. Prevotella is associated with plant-based diets. Meat and dairy have no fibre. A higher Prevotella abundance is also beneficial for regulating glycaemic control and keeping inflammatory processes within normal levels

There have been tests on the effects of the gut biome on the brain and behaviour. Indicating the relevance of gut microbiota on cognition, the first human study, done by Fernandez Real J et al, used just brain imaging and a microbial profile of the gut, and could distinguish obese from non obese individuals. The authors found that an abundance of Actinobacteria altered the  hypothalamus and the caudate nucleus.

This is important because the hypothalamus is responsible for releasing hormones, regulating body temperature, controlling appetite, managing sexual behaviour and regulating emotional responses. The caudate nucleus functions not only in planning the execution of movement, but also in learning, memory, reward, motivation, emotion, and romantic interaction.

 Acinetobacter have been isolated from soil, water, sewage, milk and chicken. Flavobacterium species prefer chilled foods such as milk, raw meats, and wild and farmed fresh-water fish (Blackburn, 2006).Both these bacteria increase in obesity.

New research argues that emotional distress and mental illnesses are linked to the role of microbiota in the gut, and can be potentially treated via microbial intervention strategies. Also, certain diseases, such as obesity, are caused by a specific microbial composition, and that a balanced gut microbiome is related to healthy ageing. In this light, it seems possible that a plant-based diet is able to influence brain function. So, you need to decide whether you want to be a Bacteroides person or a Prevotella person.

 By the way, two more reasons to turn vegan :

Do vegans pass more gas ? In the beginning they do because the gut microbiome is changing to new bacteria to digest fibre. But once the change is made then the gas becomes normal. But the smell of vegan gas is far, far, less than the pungent wind of animal eaters.

Men on a non-meat diet have been consistently judged to have a more attractive, masculine, and pleasant body odour. Meat-eaters have a more intense, less pleasant odour. This is also related to the bacteria in the gut.

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