Food and the gut
Sugar, gut health and the link to metabolic disease
Excess added sugar affects the gut and the liver directly. Fructose that the small intestine cannot absorb is fermented in the colon, causing gas and loose stools, and the fructose that is absorbed is turned into fat by the liver. Over time this contributes to fatty liver, insulin resistance and type 2 diabetes. The World Health Organization advises keeping free sugars below about six to twelve teaspoons a day.
In short
- The concern is free sugar: sugar added to food and drink, and the sugar in juices, honey and syrups. Whole fruit is not the problem.
- Sugary drinks are the most harmful form, because they deliver a large dose quickly.
- Fructose is processed by the liver, and in excess it is converted to fat.
- Jaggery and honey are still sugar.
- Artificial sweeteners are not a free pass; their effect on gut bacteria is under study.
What counts as sugar?
Table sugar is half glucose and half fructose. So are jaggery and, roughly, honey. “Free sugars” are those added by the cook, the manufacturer or you, plus the sugars in fruit juice and syrups. The sugar inside whole fruit comes packaged with fibre and water, is absorbed slowly, and is not counted.
What does excess sugar do in the gut?
It overwhelms absorption
The small intestine can absorb only so much fructose at once. The excess reaches the colon, where bacteria ferment it into gas. Many people with bloating and loose stools are sensitive to this.
It changes the diet around it
Sugary foods displace fibre-rich foods. Gut bacteria that depend on fibre decline.
It adds to reflux and weight
Large, sweet meals and drinks contribute to weight around the waist, which worsens acid reflux.
What does it do in the liver?
Almost all fructose is handled by the liver. In small amounts this is harmless. In large, repeated doses, particularly from drinks, the liver converts it to fat. Some of that fat stays in the liver, and some is released into the blood as triglycerides. This is a direct route to fatty liver and to insulin resistance, even in people who are not overweight.
What about artificial sweeteners?
They contain few or no calories, and replacing sugary drinks with them reduces sugar intake. However, an experimental study found that some sweeteners altered gut bacteria and worsened blood sugar control in mice and in some human volunteers. The findings in people are not consistent. Sugar alcohols such as sorbitol, used in sugar-free sweets and gums, commonly cause gas and loose stools.
A reasonable position: use sweeteners sparingly as a step toward less sweetness overall, not as a permanent substitute.
How much sugar is too much?
The World Health Organization advises that free sugars make up less than 10 percent of daily energy, about twelve teaspoons for an adult, and suggests that below 5 percent, about six teaspoons, brings further benefit. One 300 ml soft drink contains about seven to eight teaspoons.
Where is sugar hidden in the Indian diet?
- Tea and coffee with sugar, several times a day
- Packaged fruit juices, soft drinks and energy drinks
- Malted “health” drinks and flavoured milk
- Biscuits, rusks, cakes and breakfast cereals
- Flavoured yoghurt and lassi
- Ketchup, sauces and ready-made chutneys
- Sweets after meals as a daily habit
How do I cut down?
Start with drinks
Replace soft drinks and juices with water, buttermilk, plain soda with lime, or unsweetened tea.
Halve the sugar in tea and coffee
Then halve it again after two weeks. Taste adapts.
Eat fruit, do not drink it
Whole fruit, two servings a day.
Read labels
Sugar appears as sucrose, glucose syrup, fructose, maltodextrin, honey and “fruit concentrate”.
Keep sweets for occasions
A small portion, with a meal, not as a daily routine.
When should I see a doctor?
Ask for a check of blood sugar, triglycerides and liver enzymes if you have weight around the waist, a family history of diabetes, or fatty liver on a scan. Persistent bloating and loose stools after sweet foods can be tested with a breath test.
Questions patients ask me
Is jaggery or honey healthier than sugar?
They contain small amounts of minerals, but the body handles them as sugar. The same limits apply.
Should people with fatty liver avoid fruit?
No. Whole fruit in normal amounts is beneficial. Avoid fruit juice, and keep to two or three servings of whole fruit a day.
Does sugar feed harmful gut bacteria?
A diet high in sugar and low in fibre is associated with a less diverse population of gut bacteria. The larger effect comes from the fibre that sugary foods replace.
Do I have to give up sugar completely?
No. Staying within six to twelve teaspoons of free sugar a day, and avoiding sugary drinks, is what matters.
Sources
This page is written for patients and is based on the guidelines and studies below. It is for education and does not replace a consultation.
- Review of fructose, sugar and fatty liver disease. Jensen T et al. J Hepatol. 2018. PubMed 29408694
- Study of artificial sweeteners, gut microbiota and glucose tolerance. Suez J et al. Nature. 2014. PubMed 25231862
- American Association for the Study of Liver Diseases practice guidance on fatty liver disease. Rinella ME et al. Hepatology. 2023. PubMed 36727674
- Systematic reviews of carbohydrate quality and human health. Reynolds A et al. Lancet. 2019. PubMed 30638909