We all know eating a lot of sugar isn't great for our gut health, not to mention our waistline. But why does a sugar-rich diet cause weight gain? A new preclinical study from Columbia University's medical school, published in Cell, found that a Western-style diet (high in fats and high-fructose) alters the gut's microbiome, triggering a biological cascade of events that lead to obesity and type 2 diabetes. Specifically, high dietary sugar intake depleted the subjects' gut microbes that induce Th17 cells, a type of immune cells that help protect the body against disease-causing invaders and help regulate fat absorption across the intestinal barrier. This in turn protects the body against metabolism problems like diabetes and weight gain.

These findings underline the intricately collective effect of nutrition, microbiota health and intestinal immunity in the regulation of metabolic diseases, the authors pointed out. "Our study suggests that for optimal health, it is important not only to modify your diet but also improve your microbiome or intestinal immune system, for example, by increasing Th17 cell-inducing bacteria," they explained.

Why is sugar bad for your gut health?

The Columbia researchers found that a high-sugar, fat-focused Western diet can impact the gut microbiome. The diet was shown to deplete filamentous bacterium cells, microbiota that induce Th17 immune cells in mice's intestinal environments.

Why are these immune cells important and how are they involved in metabolic health? According to the study, Th17 cells support metabolic health by slowing the absorption of "bad" fats from the intestines and helping decrease intestinal inflammation. In contrast, low levels of these intestinal immune cells have been associated with metabolic disease, glucose intolerance, insulin resistance, inflammation and increased body weight.

The researchers also found that a high-sugar diet favored the growth of bad bacteria that replaced the immune-cell-inducing microbiota, resulting in reduced Th17 cells and an increased risk of metabolic disease. The study also revealed that sugar-free, high-fat foods did not seem to lead to negative metabolic symptoms as long as filamentous bacterium cells were present in the gut microbiome. However, when there's a lack of Th17-inducing microbiota, a low-sugar, high-fat diet resulted in weight gain and other metabolism biomarkers.

These findings suggest that excess sugar disrupts the gut's microbiome, negatively impacting gut health and leading to weight gain and other metabolism imbalances. The study also suggests that replenishing Th17-inducing microbiota with increased prebiotic and probiotic intake can help increase Th17 immune cells, prompting protection against metabolic diseases.

"Sugar eliminates the filamentous bacteria, and the protective Th17 cells disappear as a consequence," explained the authors.

Sugar, microbiome and weight gain: What's the takeaway?

Your gut microbiome—like that of mice and other animals—includes trillions of microorganisms that work in tandem with your body to encourage head-to-toe wellness. One way they do that is by encouraging Th17 immune cells that protect the body against diet-induced obesity, diabetes, and other metabolism imbalances. The presence of sugar in the gut microbiome disrupts this process by allowing overgrowth of harmful bacteria.

Of course, the gut microbiome in mice differs from that in humans, and it's still unclear which bacterium species would be optimal for inducing Th17 cells in humans. What is certain from this study is that excess sugar can alter gut microbiota, negatively impacting gut health and well-being.

Pro tip: Learning to manage sugar spikes in the blood can promote gut and microbiome health.

Good bacteria vs. bad bacteria: What’s the difference?

When we talk about "good" vs. "bad" bacteria, we're not talking about morals or ethics. We're referring to how they interact with our bodies and their effect on well-being. Following that train of thought, we can then say that it's the good gut bacteria—the trillions of microbes and bacterium cells that reside on and inside us—that are associated with a healthy gut and overall wellness.

After all, your mind and gut are intimately linked, and it's thanks to that gut-brain connection that a healthy gut means a healthy mind (due to optimal neurotransmitter and hormone balance, which affect your mood, memory and more) and a strong immune system. This, in turn, means a healthier you.

And yes, you guessed it: bad gut bacteria are the microbes and bacterium cells that, when they overgrow, result in poor health symptoms when interacting with our bodies. This can happen when our food choices lack gut-friendly foods, like:

• Prebiotics:

  Not to be confused with probiotics, prebiotics are carbohydrate-based, fiber-rich food sources for your gut microbiota.

• Probiotics:

  Are live microbes and bacterium cells, like Lactobacillus and Bifidobacteria, that can help balance and replenish the beneficial gut bacteria. Adding probiotics also helps.

• Fermented foods:

  These are gut-friendly foods that have undergone a fermentation process. Think kefir, sauerkraut, kombucha and pickled onions; incorporating these fermented foods into your meals can significantly improve gut bacterial health.

Pro tip: Balancing your gut flora by favoring good bacteria with nutrient-dense foods can help reduce cravings for unhealthy foods.

Do bad bacteria feed on sugar?

Yes, but so do the good bacteria. Let's start by defining "sugar." In a nutshell, "sugar" refers to any sweet, soluble carbohydrate. Sugars are made of building blocks called monosaccharides like glucose and fructose. When these building blocks combine, they form more complex sugars like starches and fiber. Many of these carbohydrates are naturally occurring and are for all life forms. Different cells (in all organisms) need glucose to produce ATP (cellular fuel) and perform healthily and optimally.

So, if gut bacteria need sugar, why is it bad? Well, it's not bad when we're talking about naturally occurring sugars. The problem starts when we replace natural sources like fruits, vegetables, and yogurt with highly refined and processed sugars like baked goods, fast foods, artificial sweeteners, and added sugars in foods and beverages.

Nowadays, we eat more and move less, and we develop daily habits that foster cravings for unhealthy foods over nutrient-rich choices, all of which impacts our intestinal and digestive health. In other words, indulging our sugar cravings frequently and in excess results in an overload of sugar in the microbiome, altering the gut's healthy bacterial balance, and leaving our metabolism out of whack.

Maintaining a healthy gut depends on the kind of dietary sugar you (and your gut microbiota) are eating—and always in moderation. A meta-analysis of 13 prospective cohort studies found that fresh, unprocessed fruits, juices (without added sweeteners) and plain yogurt were not associated with metabolic syndrome, and instead showed protective benefits.

How to control your sugar cravings

As you've seen so far, gut health is a cornerstone for overall wellness. And your food preferences—the quality of proteins, carbohydrates and fats—play a central role in shaping your gut microbiota, upholding that proverbial saying "you are what you eat."

Choosing nutrient-dense, low-FODMAP foods will help you feel satisfied for longer and curve cravings that show up because your body may still be hungry.

1. Drink green tea:

   Green tea is well-known for its calming amino acid L-theanine. It also contains caffeine, which boosts exercise performance and may help you burn more calories.

2. Eat the rainbow:

   Following eating patterns like the ones in the Mediterranean, flexitarian, and MIND diets can help maintain a healthy microbiome.

3. Check your hormones:

   Be proactive in staying healthy and do regular blood work to keep your thyroid in check, hormones balanced and brain neurotransmitters in order—all of which influence feelings of hunger that can result in food cravings.

4. Decompress from stress:

   Feeling frazzled and on edge can trigger food cravings, eliciting the desire to snack on comfort foods. Stay stress-free with techniques to calm yourself down like doing yoga, meditating, and affirmations; over time, it'll help you overcome cravings.

5. Prioritize sleep quality:

   Getting restful shuteye is about more than just your beauty sleep. Poor sleeping patterns impact your gut and result in increased food cravings.

Still, when there's a bacterial imbalance, sugar cravings can come up despite eating balanced meals. When those sugar cravings kick in, there are a few ways you can help control appetite cravings:

• Body movement:

  Incorporating a regular exercise routine into your daily habits can help thwart cravings by influencing hormones that promote healthy hunger-regulation. Pro tip: Combine activities like swimming, jogging, and cycling with weightlifting and resistance training to strengthen and tone muscle mass. Aim for 30 minutes a day at least five days a week.

• Appetite suppressants:

  Appetite control nutrients affect the urge to eat and can help reduce cravings by helping you feel fuller for longer. Choose high-quality, sugar-free options that use nutrients like saffron that've been shown to help modulate pathways that regulate hunger.

• Stay hydrated:

  Give your body plenty of water (and beverages without sweeteners) so you don't confuse hunger with thirst. When you drink at least 2L of water daily, it can help lower cravings and hunger signals sent to the brain.

Healthy diet, healthy microbiome, healthy weight...healthy you!

Let's recap. Your microbiome includes trillions of microbes and bacterium cells that work cohesively with your body, fostering thriving conditions for gut health and beyond. Excess simple sugars alter the delicate ecosystem in your gut, and as this preclinical study shows, it may disrupt specific groups of microbiota that induce Th17 immune cells. These immune cells confer protective effects against metabolic syndrome, affecting gut health, glucose tolerance, insulin resistance and other aspects of your health. The foods you choose can help strengthen and replenish your microbiome with beneficial gut bacteria.

References

• Alcock, Joe, et al. "Is Eating Behavior Manipulated by the Gastrointestinal Microbiota? Evolutionary Pressures and Potential Mechanisms." Bioessays. October 2014. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270213/
• Kawano, Yoshinaga, et al. "Microbiota Imbalance Induced by Dietary Sugar Disrupts Immune-Mediated Protection From Metabolic Syndrome." Cell. August 2022. https://doi.org/10.1016/j.cell.2022.08.005
• Jeong, Ji Na. "Effect of Pre-Meal Water Consumption on Energy Intake and Satiety in Non-Obese Young Adults." Clin Nutr Res. October 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6209729/
• Moszak, Malgorzata, et al. "You Are What You Eat—The Relationship Between Diet, Microbiota, and Metabolic Disorders—A Review." Nutrients. April, 2020. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7230850/
• Sanlier, Nevir, et al. "Health Benefits of Fermented Foods." Crit Rev Food Sci Nutr. 2019. https://pubmed.ncbi.nlm.nih.gov/28945458/
• Schwarz, Jean-Marc, et al. "Conversion of Sugar to Fat: Is Hepatic de Novo Lipogenesis Leading to Metabolic Syndrome and Associated Chronic Disease? J Am Osteopath Assoc. August 2017. https://pubmed.ncbi.nlm.nih.gov/28759094/
• Seminani-Axad, Zhila, et al. "Association of Major Food Sources of Fructose-Containing Sugars with Incident Metabolic Syndrome: A Systemic Review and Meta-Analysis. JAMA Net Open. July 2020. https://pubmed.ncbi.nlm.nih.gov/32644139/
• White, John R. "Sugar." Clin Diabetes. January 2018. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5775006/

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