When we think about hydration, we usually picture a glass of water. But part of the water your body gets every day comes from food: fruit, vegetables, soups, beans, rice. On treatment with a GLP-1 medication, when appetite drops and plates get smaller, that share drops too.

In this article, you’ll learn why water deserves more attention during this phase and find simple ideas to keep up the habit throughout the day.

The water that comes from your plate

The European Food Safety Authority (EFSA) published reference values for water intake in 2010. For adults, adequate total water intake was set at about 2.0 liters (roughly 68 fl oz) a day for women and 2.5 liters (roughly 85 fl oz) a day for men, under mild temperatures and moderate physical activity.

One important detail: these values include all of the day’s water, from drinks and from food itself. In other words, someone eating much less than before loses part of that contribution without noticing, and may need to pay more attention to what they drink.

These numbers are references for the population, not an individual target. Each person’s needs change with heat, physical activity, body size and health. Some conditions, such as certain heart and kidney diseases, may call for fluid limits. That’s why the right amount for you should be discussed with your doctor.

Why it matters during treatment

Gastrointestinal effects such as nausea, vomiting and diarrhea are common early in GLP-1 treatment. Besides being uncomfortable, they make the body lose fluids.

The U.S. prescribing information for semaglutide for weight management includes a warning about acute kidney injury associated with volume depletion, and instructs doctors to monitor kidney function in people who report side effects that could lead to that loss. It’s an uncommon event, but it shows why hydration is worth looking after, especially on days with gastrointestinal symptoms.

Signs you may be short on water

Watch for signs such as:

strong thirst or a very dry mouth;
dark urine or very little of it;
dizziness, especially when standing up;
unusual tiredness;
a headache with no other explanation.

If you’re vomiting or have diarrhea and can’t keep fluids down, or if these signs show up and don’t improve, see your doctor.

Ideas for drinking water throughout the day

With a more sensitive stomach, large amounts at once can be uncomfortable. It usually works better to spread water across the day:

Keep a bottle within reach. On your desk, in your bag, in the car. Seeing the bottle is a reminder to drink.
Take small sips. Several sips over an hour sit lighter than one big glass at once.
Use reminders. A phone alarm, or tie a glass of water to fixed moments, like when you wake up, before you leave home and after your shower.
Vary the flavor. Slices of lemon, orange or cucumber, or mint leaves make water more interesting.
Unsweetened teas count too. If they have caffeine, like black tea or yerba mate, don’t overdo it.
Go easy on carbonated drinks. They can add to the discomfort when your stomach is sensitive.

Foods that hydrate too

Even with a smaller appetite, you can choose foods that add water:

Fruit such as watermelon, melon, oranges and pineapple;
Vegetables and greens, raw or cooked;
Soups and broths, which can also include beans, lentils or shredded chicken for added protein;
Plain yogurt, which brings fluid and protein at the same time.

Water and meals

Some people feel full faster when they drink a lot of liquid with their food. If that’s you, try drinking more between meals and less during them. That leaves room for food, especially protein, without letting hydration slide.

Tracking helps

Writing down how much you drink for a few days often reveals a pattern: many people are surprised at how little they drink on busy days. Logging water along with meals and symptoms also helps you see whether queasy days line up with low-fluid days, useful information to bring to your appointment.

Water seems like a small thing, but it’s one of those simple habits that make a difference in the day-to-day of treatment.

Sources

EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific Opinion on Dietary reference values for water. EFSA Journal, 2010.
U.S. Food and Drug Administration. Wegovy® (semaglutide): prescribing information. FDA.
Gorgojo-Martínez JJ, et al. Clinical Recommendations to Manage Gastrointestinal Adverse Events in Patients Treated with Glp-1 Receptor Agonists: A Multidisciplinary Expert Consensus. Journal of Clinical Medicine, 2023.

Hydration: why water matters more when you're eating less