Why You Might Feel Tired While Losing Weight

Quick answer: Feeling tired while losing weight is common. The usual reasons are eating less energy overall, not getting enough protein or iron, poor sleep, and not drinking enough. On a GLP-1 like Mounjaro or Wegovy, tiredness can also be a side effect of the medicine itself. Small changes to eating, drinking and sleep often help, but tiredness that lasts more than a few weeks is worth a GP check, including a blood test.

Common reasons you feel tired

1. You're eating less energy

Weight loss needs a calorie deficit, and your body notices. A big drop in food intake, especially early on, can leave you feeling flat. A steadier, more moderate approach usually feels better than a sharp cut.

2. Protein has slipped

With a smaller appetite, protein is often the first thing to go. Our guide to getting enough protein on Mounjaro has practical ways to keep it up.

3. Low iron

Iron is one of the most common nutrient gaps in the UK, especially in women who have periods. Iron contributes to the reduction of tiredness and fatigue, and low iron is easy to check with a simple blood test from your GP.

4. Not drinking enough

Around a fifth of our fluid comes from food, so eating less can quietly lower your fluid intake. Even mild dehydration can make you feel tired and headachy. See our guide to hydration on a GLP-1.

5. Poor sleep

Hunger, stress and changes in routine can all disturb sleep, and poor sleep makes the next day harder. A consistent bedtime and a wind-down routine make a real difference.

6. The medicine itself

Fatigue is a listed side effect of some GLP-1 medicines, particularly when starting or after a dose increase. Supplements aren't a treatment for medication side effects. If tiredness is affecting your daily life, speak to your prescriber.

Nutrients linked to energy

These nutrients contribute to the reduction of tiredness and fatigue:

• Iron: red meat, pulses, dark green vegetables, fortified cereals
• Magnesium: nuts, seeds, wholegrains, leafy greens
• Vitamin B6 and B12: fish, eggs, dairy, poultry, fortified foods

If your diet has become very limited, a multivitamin such as our Women's Multivitamin & Minerals can help fill the gaps. For magnesium specifically, see Magnesium 6 in 1 Advanced Complex.

Quick wins for more energy

1. Eat something with protein within a few hours of waking.
2. Sip fluids steadily through the day.
3. Get outside in daylight, especially in the morning.
4. Take a short walk after meals.
5. Keep your bedtime and wake time consistent.

When to see your GP

• Tiredness lasting more than a few weeks
• Feeling breathless, dizzy or very pale
• Unexplained weight loss beyond what you're aiming for
• Low mood, or losing interest in things you enjoy

FAQs

Why am I so tired on Mounjaro?

It's often a mix of eating less, lower protein or iron, fluid intake and the medicine itself. Speak to your prescriber if it's affecting daily life.

Is it normal to feel tired when losing weight?

Some tiredness is common, especially early on. It shouldn't be severe or long-lasting.

What vitamins help with tiredness?

Iron, magnesium, vitamin B6 and vitamin B12 all contribute to the reduction of tiredness and fatigue. A blood test can show if you're low in any of them.

Reviewed by John Lebach (Nutrition Coach) and Numan Caan (Senior Sports Scientist)

---

This article is for general information only and isn't medical advice. Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle. If you take prescribed medication, are pregnant or breastfeeding, speak to your GP or pharmacist before starting a supplement.