A stomach that is flat in the morning and swollen like a balloon by evening, constipation that lasts for days, burning that rises towards the chest after a meal, a sudden need for the toilet in the middle of a meeting… Digestive complaints may not be life-threatening, but they can affect every hour of the day. Most people look for the answer in cutting out a food entirely or starting a new supplement; yet the source of the problem is usually not a single food but the eating pattern as a whole.

On this page we explain how bloating, gas, constipation, reflux and a sensitive gut relate to nutrition, the principles of eating that support gut health, when a low-FODMAP diet helps, and which symptoms mean you should see a doctor without delay.

Why is the digestive system so easily affected?

The digestive tract is not just a tube that breaks down food. It has its own network of nerves, is in constant communication with the brain and is home to a community of trillions of bacteria, the gut microbiota. That is why your digestion is affected not only by the food on your plate but also by your sleep, your stress level, how much you move, how fast you eat and the medicines you take.

The student who gets diarrhoea during exam week and the person who becomes constipated on holiday are everyday examples of this connection. This is why, when a nutrition plan is prepared, the question is not only “what do you eat”; the flow of the day, meal times, toilet habits and when the complaint gets worse are all assessed too.

Common digestive complaints and their link with nutrition

Bloating and gas

Some gas during the day is a natural result of digestion. The most frequent causes of uncomfortable bloating are eating quickly and swallowing air, going hungry for a long time and then eating a lot in one meal, constipation, fizzy drinks and carbohydrates that ferment easily in the gut. Onions, garlic, pulses, some fruits, milk and the sweeteners in sugar-free gum belong to this group.

Another common situation is this: someone decides to improve their diet, suddenly increases salad, wholegrain products and pulses, and then has more gas. This does not show that the diet is wrong; it shows that the gut needs time to get used to the new amount of fibre.

Constipation

Constipation does not only mean going to the toilet infrequently. A range from three times a day to three times a week is generally considered normal; what really matters is the consistency of the stool, the need to strain and the feeling of complete emptying. Someone who goes every day but passes hard stools, strains for a long time or does not feel emptied may also be constipated.

Too little fibre and fluid, inactivity, putting off the urge to go, skipping meals and some medicines make constipation worse. When constipation does not improve despite a high fibre intake, the problem is usually the type of fibre, fluid intake or slow bowel movement; increasing fibre further can make things worse.

Reflux and heartburn

When stomach contents flow back into the oesophagus, they cause burning in the chest, a sour taste in the mouth and belching. In some people it shows itself without burning, as hoarseness, constant throat clearing and a dry cough. Large portions, fatty and fried foods, lying down straight after eating, eating late and excess fat around the waist make reflux more likely. Coffee, chocolate, mint, tomatoes, spices and alcohol are often named as triggers; but which of them affects you is personal, and not everyone needs to follow the same list.

Irritable bowel syndrome

This is a condition in which abdominal pain is accompanied by bloating, diarrhoea, constipation or an alternation of the two, with no structural disease found on investigation. It is diagnosed by a doctor. Nutrition plays an important part in managing symptoms: regular meals, the right type of fibre, limiting caffeine and alcohol and, where needed, a low-FODMAP approach can ease complaints. Stress management and sleep are also inseparable parts of treatment.

Principles of eating that support gut health

Whatever the complaint, there are some basic principles that help the gut work regularly. Not all of them apply to everyone to the same degree; the plan is shaped by the person’s symptoms and tolerance.

Increase fibre gradually. Around 25–30 grams of fibre a day is recommended for adults, but most people fall well short of this. Reaching the target over several weeks rather than one reduces gas and bloating.
Pay attention to the type of fibre. The soluble fibre in foods such as oats, psyllium husk, flaxseed, carrots and courgettes holds water, softens the stool and is generally better tolerated by a sensitive gut. Insoluble fibres such as bran may increase bloating in some people.
Eat a wider variety of plants. Rather than always eating the same three vegetables, including different vegetables, fruits, pulses, whole grains, nuts and herbs during the week can support the diversity of gut bacteria.
Make room for fermented foods. Foods such as yoghurt, kefir, ayran and home-made pickles contain live bacteria. In people who tolerate them, regular consumption can contribute to the gut flora.
Drink enough fluid. Fibre works together with water. Increasing fibre while fluid intake is low can make constipation worse rather than better.
Eat slowly and chew well. Digestion begins in the mouth. A meal finished in five minutes in front of a screen increases both swallowed air and the size of the mouthfuls reaching the stomach.
Keep regular meal times. The gut likes rhythm. Eating at irregular hours and large meals after long periods without food increase bloating and reflux.
Move. Even a ten-minute walk after a meal stimulates bowel movement and helps gas to pass.

Who is the low-FODMAP diet suitable for?

FODMAP is the collective name for short-chain carbohydrates that are not fully absorbed in the small intestine and are rapidly fermented in the large intestine. The low-FODMAP diet is a three-stage method used particularly in irritable bowel syndrome, after a medical diagnosis:

Restriction: Foods high in FODMAPs are reduced for a few weeks.
Reintroduction: Food groups are added back one at a time in increasing amounts, and it is observed which ones cause symptoms.
Personalisation: Only the foods and amounts that cause trouble are limited; everything else returns to the diet.

This diet is not a permanent way of eating. Staying in the first stage for a long time both narrows the diet and reduces the fibres that feed gut bacteria. Because managing a wide list that runs from onions and garlic to pulses is difficult, it is recommended that the process be carried out with a dietitian. For the approach used when symptoms are linked to a single food, see the food intolerance and elimination diet page.

What you should know about probiotics and supplements

Probiotics are live micro-organisms that can benefit health when taken in adequate amounts. Their effects, however, are specific to the species and strain: a bacterium that works in one product may not give the same result as one in another, and not every digestive complaint calls for a probiotic. Rather than using a randomly chosen product for months, it is better to ask your doctor or dietitian whether you need one and which product would be suitable.

The same principle applies to fibre supplements, magnesium and digestive enzymes. A supplement does not take the place of an eating pattern; it can interact with your medicines and may mask some symptoms and delay diagnosis.

Common mistakes with digestive complaints

Cutting out a whole food group by trial and error: Giving up gluten or dairy at random may bring temporary relief but can hide the real cause and narrows the diet unnecessarily.
Turning to “colon cleanses” and detox programmes: The gut does not need separate cleansing. Liquid-based or laxative programmes can cause loss of fluid and minerals.
Making a habit of laxative herbal teas: Long-term use of stimulant herbs such as senna without medical advice is not recommended.
Raising fibre all at once: One of the most common causes of gas and bloating.
Going hungry all day and making up for it in the evening: A large meal eaten late increases both reflux and morning bloating.
Blaming food alone: The picture is incomplete unless sleep, stress, inactivity and medicines are taken into account.

When should you see a doctor?

If you have any of the following, see a doctor without waiting for dietary changes:

Blood in the stool, or black, tarry stool
Unintentional and unexplained weight loss
Abdominal pain or diarrhoea that wakes you at night
Difficulty swallowing, a feeling of food sticking, repeated vomiting
A new change in bowel habit that lasts for weeks
Anaemia, fever or pain that keeps getting worse
A family history of bowel cancer, inflammatory bowel disease or coeliac disease

Frequently asked questions

I started eating healthily and my gas increased. Is that normal?

Usually, yes. When the amount of vegetables, pulses and whole grains rises quickly, gut bacteria ferment more fibre and gas increases. Increasing fibre gradually, soaking pulses and cooking them well, and drinking more fluid make this period easier. If the complaint lasts for weeks, it needs to be assessed.

Am I constipated if I do not go to the toilet every day?

Not necessarily. Someone who goes every other day without straining and feels fully emptied is not considered constipated. On the other hand, someone who goes every day but passes hard stools or strains for a long time may be.

Should I take probiotics?

Not everyone needs a probiotic supplement. Fermented foods such as yoghurt and kefir are a good start for most people. If a supplement is being considered, ask your doctor or dietitian which product suits your complaint.

I have reflux. Which foods should I avoid?

There is no single list of banned foods that applies to everyone. Making portions smaller, not lying down for at least two to three hours after eating and bringing the evening meal forward are more effective than food restriction for most people. Keeping a diary is the best way to identify the foods that affect you.

Does gut health affect weight loss?

Constipation and bloating can temporarily change the number on the scales and your waist measurement, but this is not an increase in fat. A digestive system that works regularly makes it easier to follow a nutrition plan; weight management, however, requires a separate and holistic assessment.

Nutrition for Digestive and Gut Health