Susie's Hydration Rules: Why GLP-1 Users Are Quietly Dehydrated

By Nutritionist Susie · 2025-03-15

GLP-1s blunt your thirst signal — and most of my clients are walking around mildly dehydrated without realising. Here's the simple electrolyte and water plan I use to fix the headaches, fatigue and constipation that come with it.

Susie here. I want to talk about the most under-rated, least glamorous fix in GLP-1 nutrition: water and electrolytes.

I'd estimate 8 out of 10 of my clients on Ozempic, Wegovy or Mounjaro come to me mildly dehydrated. They don't feel thirsty (the drug blunts that), so they drink less. They eat less, so they get fewer electrolytes from food. And then they wonder why they have headaches, foggy thinking, leg cramps and constipation.

Sort the water and the salts and you'll feel dramatically better within 4–5 days. I've watched it happen many, many times.

Why GLP-1s dehydrate you

Three quiet reasons:

1. Blunted thirst. You no longer get the "I'm thirsty" nudge as strongly. By the time you remember to drink, you're already behind.
2. Less food = fewer electrolytes. Most of your sodium, potassium and magnesium normally comes from food. Eat half as much, get half as much. Simple maths.
3. Side-effect losses. Even mild nausea, loose stools or extra bathroom trips chip away at your fluid balance.

Susie's daily fluid target (the simple version)

For most adults on a GLP-1, aim for:

• 30–35 ml of fluid per kg of body weight per day
• That's about 2 to 2.5 litres for most people
• More on training days or hot weather — add 500 ml per training session

You don't need to chug it. You need to sip it consistently, every 20–30 minutes, between meals.

The 3 electrolytes you actually need

Forget fancy bottles for a moment. There are only three minerals that matter day-to-day:

1. Sodium — the one everyone under-eats Target 2–3 g of sodium per day (that's about ½ to 1 teaspoon of salt). Add a pinch to your water bottle or get it from broth, olives, miso, salted nuts.

2. Potassium — the muscle and mood mineral Target 3–4 g per day. Easiest sources: banana, kiwi, avocado, white beans, spinach, plain yogurt, salmon. One avocado + one banana already gets you halfway.

3. Magnesium — the one that fixes your sleep and constipation Target 300–400 mg per day. Best food sources: pumpkin seeds, dark chocolate (yes really), spinach, black beans, almonds. If you struggle to get it from food, magnesium glycinate at night is a quiet game-changer for sleep and bowel regularity.

My go-to GLP-1 hydration routine

This is what I tell almost every client:

• On waking: 500 ml of water + a pinch of sea salt + squeeze of lemon. Set the day up.
• Mid-morning: A herbal tea or a glass of water with each medication.
• With lunch: Sip, don't chug — sipping won't fill you up too fast.
• Mid-afternoon: A bottle with a low-sugar electrolyte tab if you're flagging or training that day.
• Evening: Slow it down by 7pm so you sleep through.

When to use an electrolyte sachet

You don't need one every day. Use one when you:

• Trained (especially anything sweaty)
• Are travelling or in heat
• Had a nauseous day and ate very little
• Wake up with a headache or mid-afternoon brain fog

Look for sachets with at least 500 mg sodium and less than 5 g of sugar. Anything ultra-sweet is a sports drink in disguise.

Signs you're winning at hydration

You'll know it's working when:

• Your wee is pale yellow (sorry, but that's the cleanest test)
• The 3pm fatigue dip stops happening
• Headaches reduce
• Bowels move regularly (a hugely under-discussed GLP-1 win)
• Skin looks better — yes, really

The mindset shift

Stop waiting to feel thirsty. On a GLP-1, your thirst signal is unreliable. Treat hydration like a scheduled habit, not an instinct. Carry a 750 ml bottle, refill it three times a day, add salt at breakfast, and get your potassium-rich foods on the plate.

Do this for two weeks and you'll be amazed how much of the "GLP-1 fatigue" was just dehydration in disguise. — Susie