In today’s post I’ll be discussing the gut microbiome and its role in weight management. Why is it that two people can consume the same diet, engage in the same amount of activity, and still have entirely different responses to food? It turns out that some of this discrepancy can be explained by the type and amount of good and bad gut bacteria we have living in our gastrointestinal systems. If you haven’t read my post on the gut microbiome, you may want to start there!

The composition of your individual gut microbiome is partially determined by genetics. However, based on twin studies, environmental factors- like dietary patterns are far more instrumental in determining the type, and quantity of bacteria that make up our microbiome. Theoretically, this is great news, we are not necessarily stuck with the microbiome we inherited. Unfortunately for those of us in the US, our diet (high in animal-based protein and saturated fat) is not very gut friendly- it leads to decreased microbial diversity and function. These conclusions were based on studies of microbial changes noted in people emigrating to the US, which also revealed a 4-fold increase in the risk of obesity within 15 years of emigration to the US compared with populations that stayed in their home country.

Gut bacteria, fiber and short chain fatty acids:

Lactobacillus and bifidobacterium (gut bacteria) are involved in the creation of short chain fatty acids (SCFA) such as butyrate. This is completed through the breakdown of long chains of sugar molecules (complex carbohydrates) that we are unable to digest on our own- ie. resistant starch and fiber. The resultant SCFAs participate in many signaling pathways- including their action as chemical messengers that:

1. Help increase energy expenditure
2. Decrease food intake and
3. Increase the expression of leptin (the satiety/fullness hormone)

(OMG THIS IS HOW FIBER HELPS WITH “WEIGHT MANAGEMENT”)

SCFAs such as butyrate decrease hunger, decrease the production of fat and increase its breakdown.  The conversion of fiber into SCFAs also promotes microbial diversity, which inhibits weight gain. Oral supplementation of butyrate in mice fed a high fat diet was shown to decrease food intake and combat diet-induced obesity, high insulin, high triglycerides and even fatty liver disease. It also increased the breakdown and usage of fats and activated brown fat (which breaks down fat to generate heat- this is important in temperature regulation, especially in babies). Higher concentrations of brown fat are associated with a positive metabolic effect.

Gut microbiome diversity, gene count and restoring microbial richness:

Studies have shown that individuals with low microbial gene count have more systemic inflammation, adiposity (fat), insulin resistance, and high cholesterol. Low gene count individuals gained more weight over time. Their predominant bacterial strains included Bacteroides and Ruminococcus genera.  While lean individuals had high gene counts including Bifidobacterium, Lactobacillus, and Akkermansia. Interestingly, some studies suggest that following an energy-restricted diet for as little as 6 weeks may positively impact microbial diversity.

Akkermansia muciniphila:

Akkermansia muciniphila is a probiotic that has been shown to reverse high fat diet induced weight gain and insulin resistance (in mouse models). Similar results were noted with the administration of a prebiotic known as fructo-oligosaccharide (FOS) through the enhancement of Akkermansia.

(This basically means we want Akkermansia Muciniphila in our gut microbiome and FOS are prebiotics that help to increase them, read below for more ways to naturally increase concentrations of this beneficial bacteria.

Additional strategies to increase Akkermansia include:

1. Consumption of polyphenol-rich cranberry extract (only studied in mouse models)
   
2. Participation in a 6-week caloric deficit

Human studies in overweight/obese individuals showed that daily supplementation with Akkermansia was also found to improve insulin sensitivity and decrease body weight.

In mouse fed a high-fat/high-sucrose diet, polyphenol-rich cranberry extract was found to protect against metabolic syndrome and intestinal inflammation by increasing the relative abundance of Akkermansia.

Studies of patients pre and post operatively from Roux-en-Y gastric bypass (weight loss surgery) have shown significant changes in the gut microbiome post operatively including a rapid and sustained increase in Akkermansia. (If I had to guess the mechanism of action here, my thought would be the significant caloric restriction that happens after weight loss surgery, though there could be many different factors at play.)

Excess carbohydrate intake and Candida overgrowth:  

Excess carbohydrate intake may be the biggest dietary predictor of low microbial diversity. Diets that are high in total carbohydrates and sugar are also associated with increased Candida (fungal/yeast) levels.  Elevated levels of Candida foster the growth of harmful bacterial strains, which increase the creation of less desirable SCFA- such as acetate. This SCFA increases host adiposity, while simultaneously decreasing microbial diversity. Candidal overgrowth is also associated with antibiotic use. A healthy microbiome, including lactobacillus species, will prevent the overgrowth of Candida. Diet therapy for candidal overgrowth includes avoidance of:

1. Foods high in simple sugars and starch
2. Cured and fatty meats
3. Milk and dairy products
4. Alcohol

Intermittent fasting

We have two main types of fat in our body- white and brown. When we engage in excessive caloric intake, fat is stored in white adipose tissue. On the other hand, energy expenditure via the breakdown of fats is primarily from brown adipose tissue in the form of thermogenesis (a process by which we create heat). Studies have shown that intermittent fasting (eating in a restricted time period) can cause “beigeing” of white adipose tissue.

This results in a shift in the gut microbiome that increases the production of SCFAs that help to reverse diet-induced obesity. Benefits may be seen with feeding windows as large as 8 hours daily, though longer fasting windows may demonstrate greater benefit.

This is now the second time I’ve mentioned periodic fasting as beneficial for our health, remember it also increases NAD+

Give me all the Akkermansia!

I know many of you have taken to google now and are looking for a probiotic that contains Akkermansia, there is one out there. I think their data (at the time that I am publishing this article) is still pre-clinical (lab animals, not yet humans). There are human trials underway and, from what I have read, no significant safety concerns exist with proper use.

For those considering an Akkermansia containing probiotic, they can be very pricey. While there is benefit in usage for people with low levels of Akkermansia, I am not sure that supplementing in people with normal levels would be beneficial. It may be advisable to start with gut microbiome testing, so you have a reference point and baseline levels.

When it comes to lactobacillus and bifidobacterium- these are widely available and much more affordable, you can probably get away with supplementing without checking levels first.

As always be sure to consult with your doctor for more information on what probiotic strain is best for you.

I hope this information has been helpful and I wish you the best on your journey to a healthy happy gut, it really is the (not so secret) secret to solving all your problems!

Sincerley,
Corsano MD- Your friendly neighborhood PCP

Resources: Strategies to promote abundance of Akkermansia muciniphila, an emerging probiotics in the gut, evidence from dietary intervention studies (Journal of functional foods, 2017)