Gut instinct: The link between obesity and diabetes

The gut is home to a wide variety of bacteria that impact how food is digested and nutrients are used in the body. Any variation in the gut ecosystem also impacts weight and blood sugar levels. Lifestyle changes, timely treatment, and surgical interventions in specific cases are vital, writes Dr Ashish Gautam.

People often talk about obesity and diabetes together, but gut health sits at the centre of both. The gut shapes how the body breaks down food, stores fat, and regulates blood sugar. When it falls out of balance, weight increases and blood sugar becomes harder to control.

Where the problems start

The gut is home to a large community of bacteria that affect how food is broken down and how energy is used. These organisms change how the body absorbs nutrients and responds to insulin. When their balance shifts, the body begins storing more fat, insulin stops working as well, and low-grade inflammation develops.
This is the work of the gut microbiome, the trillions of microorganisms in the intestine that function like a metabolic organ. In people with obesity, there is reduced microbial diversity, a higher ratio of firmicutes to bacteroidetes, and a rise in opportunistic species. This matters because some gut bacteria extract more calories from the same food. They break down fibre and other hard-to-digest carbohydrates to produce short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate. These increase energy availability and can lead the liver to produce more fat. Over time, this results not just in weight gain, but in metabolic changes that are harder to reverse.

How eating habits affect gut balance

Processed foods, refined carbohydrates, and added sugars reduce the diversity of gut bacteria. Low fibre intake weakens the bacteria that support digestion and metabolic regulation. The body then handles calories less efficiently and stores more than it should. Hunger signals grow unreliable and intake rises without any real sense of fullness.

Gut bacteria regulate appetite through hormones. They stimulate GLP-1 (glucagon-like peptide-1) and PYY (peptide YY), which signal fullness, while suppressing ghrelin, which drives hunger. When these bacteria are out of balance, satiety weakens and people eat more, often without realising it. Access to good food is also part of the problem. The State of Food Security and Nutrition in the World report from 2024 found that 55 percent of Indians cannot afford a healthy diet. Foods high in fat, salt, and sugar are cheap and widely available. Poor diet quality combined with excess calories keeps disrupting gut function across large sections of the population.

What the gut does to blood sugar

The gut produces hormones that regulate insulin and blood sugar. When those signals are disturbed, glucose control suffers. Chronic inflammation makes it worse by driving insulin resistance over time, a direct path to type 2 diabetes. Much of this inflammation begins with what is known as a leaky gut. When the intestinal barrier weakens, lipopolysaccharides (LPS), and toxic components from bacterial cell walls pass into the bloodstream and trigger a persistent, low-grade inflammatory response. This LPS translocation is a key driver of insulin resistance and metabolic syndrome. The rise in type 2 diabetes, including among younger
adults, closely follows this pattern. Abdominal obesity, disrupted gut function, and insulin resistance tend to develop together.

Beyond inflammation, gut bacteria also influence metabolism through signaling receptors. SCFAs activate G-protein-coupled receptors GPR41 and GPR43, and modulate AMPK, an enzyme that governs the balance between fat oxidation and fat storage. When this signaling is disrupted, the body shifts further toward storing
rather than burning energy.

Why belly fat is a different problem

Fat stored around the abdomen behaves differently from fat elsewhere. It releases compounds that worsen both inflammation and insulin resistance. Two people with the same BMI can have very different levels of metabolic risk. Waist circumference and other metabolic markers often give a clearer picture. ICMR data from 2023 shows that many adults now carry excess abdominal fat, which is closely linked to
diabetes and related metabolic changes. The gut also influences where fat is stored. Gut microbiota suppress fasting-induced adipose factor (FIAF), a protein that normally limits lipoprotein lipase (LPL) activity. When FIAF is reduced, LPL activity rises, leading the body to store more fat in adipose tissue instead of using it for energy.

Gut bacteria also modify bile acids, turning them into signaling molecules that act on FXR (farnesoid X receptor) and TGR5 receptors. These receptors influence glucose metabolism and energy expenditure. When bile acid signaling is disrupted through dysbiosis, both blood sugar regulation and calorie burning are affected.

The habits that keep it going

High sugar intake, low fibre, irregular meals, and physical inactivity all disrupt gut health and metabolism. The World Health Organisation estimates that nearly half of Indians do not meet recommended activity levels. Poor sleep affects appetite and blood sugar regulation directly. Chronic stress alters gut function and eating behaviour over time. These are not minor factors. They shape metabolic health steadily and cumulatively.

When changes to your lifestyle are not enough

Making changes to your lifestyle is a good place to start, but they don't always work on their own. For individuals who persist in their struggles despite sustained effort, medical interventions become pertinent. When a person's BMI is over 29 and they have diabetes or high blood pressure, or over 35 regardless of other conditions, bariatric surgery is a medically accepted option. These surgeries make the stomach
smaller and change the hormonal signals that control hunger and how the body responds to insulin.

Laparoscopic and robotic-assisted techniques have made these surgeries more accurate, cut down on recovery time, and cut down on complications. Some of the benefits seem to come from changes in the gut microbiome itself. Changes in gut microbes after surgery are increasingly linked to better blood sugar control and improved metabolism. Long-term data from the ARMMS-T2D study supports this, showing sustained weight loss and improved glycaemic control years after surgery.

New studies are also looking at the microbiome more closely by using dietary changes, specific probiotics, and experimental methods like microbiota transplantation. The evidence is still coming in, but the direction is clear. There are many ways that gut health, obesity, and diabetes are related.

Treating any one of them alone usually only works partially. Food, exercise, sleep, and medical care all need to work together. Taking care of your gut is not a side issue when it comes to losing weight and controlling diabetes. It should be the main point of the conversation.

(The author is principal director, robotic and laparoscopic surgery at a Delhi hospital.)