1. Food poisoning and gastroenteritis

Heat is bacteria's best friend. A recent meta-analysis calculated that, for every degree the ambient temperature rises, the risk of Salmonella or Campylobacter infection increases by about 5%; that's why bacterial gastroenteritis peaks in summer. ¹ Add eating out, a cold chain that breaks (the beach cooler, the car, the picnic) and egg-based sauces, and it's clear why this is the season of food poisoning.

If gastroenteritis strikes anyway, the main thing is to rehydrate (water and oral rehydration salts), eat a bland diet as tolerated and be patient: most cases resolve on their own within a few days. Antibiotics are rarely needed, and overusing them favors resistant bacteria and antibiotic-associated diarrhea.

2. Anisakis: watch out for raw fish

Anisakis is a larva present in many fish that, if swallowed alive, can cause severe abdominal pain and allergic reactions. Summer is its high season: marinated anchovies, ceviche, sushi, sashimi, marinades… But it's easy to prevent, because freezing and heat kill the larva. ⁵

When eating out you can relax a bit: in Spain, restaurants are legally required (Royal Decree 1420/2006) to freeze the fish they serve raw or nearly raw. ⁶ And it works: in Madrid, after 20 years of this law, anisakis sensitization (IgE antibodies) in blood donors fell from 11.6% to 2.2%, a drop of more than 80%. ⁷

3. Traveler's diarrhea

It's the most common health problem for travelers, caused by contaminated water or food. Prevention: bottled water with the seal intact, avoid ice of dubious origin, and the classic rule "boil it, cook it, peel it… or forget it." I have a dedicated guide on traveler's diarrhea. ⁸

If it appears, the basis is to rehydrate. Loperamide helps "stop" the diarrhea for a journey, but should not be used alone if there is blood in the stool or high fever. Antibiotics are reserved for moderate or severe cases (azithromycin is usually first choice), not for mild diarrhea. ⁸⁹

4. Reflux and heavy digestion

Summer is the perfect storm for heartburn: alcohol, large and late dinners, terrace cigarettes and lying down straight after. Alcohol also plays its own role: a meta-analysis linked it to a 48% higher risk of reflux, and the risk rises with drinking frequency. ¹¹

The measures that really work (ACG 2022 guideline and lifestyle reviews): don't eat in the 2-3 hours before lying down, don't lie down after eating, moderate alcohol, and raise the head of your bed if you have nighttime reflux. ¹⁰¹² If the burning is frequent, check whether it's reflux, peptic esophagitis or functional heartburn (burning with normal tests).

5. Hydration, heat and constipation

On holiday, many people get constipated: a change of routine and schedule, less fiber, and above all dehydration from the heat and sweating. As a reference, EFSA sets adequate water intake (including from food) at about 2 litres/day for women and 2.5 for men, and in summer you need more. ¹³

Hydration is a protective factor against constipation, and fiber (fruit, vegetables, legumes) is the first-line treatment; just increase it gradually. ¹⁴ A key detail: fiber without enough fluid can make constipation worse. In one trial, adding 1.5-2 litres of water a day to a high-fiber diet increased bowel movements and reduced laxative use. ¹⁵

6. Holiday alcohol: liver, pancreas and stomach

In summer, drinking concentrates and "binge drinking" appears: in Spain it's defined as 6 or more drinks (60 g of alcohol) in men or 4 or more (40 g) in women on a single occasion. Low-risk limits are low: about 20 g/day for men and 10 g/day for women (one standard unit ≈ a small beer or a glass of wine). ¹⁸ And it's worth remembering that the WHO is blunt: there is no safe amount of alcohol for health (it's classified as a Group 1 carcinogen). ¹⁷

For the digestive system, a drinking binge can take its toll in several ways:

• Pancreas: above about 4 drinks a day the risk of pancreatitis soars (at ~8 drinks/day it multiplies by four). A binge can trigger acute pancreatitis.¹⁹
• Esophagus/stomach: forceful vomiting after drinking can produce a tear (Mallory-Weiss syndrome), a frequent cause of upper GI bleeding.²⁰ Alcohol also worsens reflux and gastritis.
• Liver: heavy drinking worsens fatty liver; if you already have liver disease, the safe margin is even smaller.

7. Hepatitis A

Hepatitis A is transmitted by the fecal-oral route: contaminated water or food (often raw or undercooked shellfish, such as bivalves) or direct contact. It causes fever, tiredness, nausea, abdominal pain, dark urine and jaundice; it usually resolves on its own, but it can leave you unwell for weeks. ²¹

The virus survives freezing and needs more than 85 °C to be inactivated, so with shellfish the key is to cook it well. If you travel to higher-risk areas (parts of Africa, Asia, Central and South America), vaccination is recommended: it's a very effective vaccine. ²²

8. Traveling with a chronic digestive disease

If you have irritable bowel syndrome (IBS), inflammatory bowel disease, celiac disease or reflux, a little planning lets you enjoy summer just the same:

• Medication in your carry-on, with its prescription and in sufficient quantity; be careful storing heat-sensitive drugs.
• Pre-travel consultation if you have inflammatory bowel disease or are immunosuppressed: vaccines need reviewing (live-virus ones are usually contraindicated) and a standby antibiotic for traveler's diarrhea may be considered. Get good insurance.²³
• Celiac disease: always carry gluten-free snacks (options are limited at airports and service stations), request the gluten-free meal when booking your flight/train and reconfirm it, and use translated cards explaining your diet.²⁴

My approach in the clinic

Related reading (to complete the picture)

Traveler's diarrhea

Prevention, first-aid kit and when to use antibiotics.

Read post →

Abdominal bloating

Beer, eating out and gas: why you bloat in summer.

Read post →

Fatty liver

Holiday alcohol and how to take care of your liver.

Read post →

FAQ: quick summer questions