Eat less, butWhy this matters on a GLP-1
Peptides like semaglutide and tirzepatide suppress appetite hard. When you’re eating a fraction of what you used to, three things tend to slip:
- Micronutrients — less food means fewer vitamins and minerals coming in.
- Protein & muscle — rapid weight loss can strip lean muscle if protein drops too low.
- Hydration & electrolytes — reduced intake plus GI side-effects can leave you low.
None of the below is a prescription — it’s the stuff people and clinicians commonly pay attention to. Get bloodwork and talk to your doctor before supplementing; more isn’t better, and some of these (like iron) can be harmful if you’re not actually low.
The shortlist
Energy metabolism
Vitamin B-Complex
Provides the full set of B vitamins your body uses to convert food into energy. When you’re eating much less, B intake drops — and Bs are among the first to run short.
Fatigue & immunity
Vitamin D3
Low vitamin D is a very common cause of fatigue, and many adults are low regardless of diet. Worth testing — a lot of people benefit from supplementing if their levels are genuinely low.
Muscle · sleep · energy
Magnesium (glycinate or malate)
Supports muscle function, recovery, sleep quality and energy metabolism. The glycinate and malate forms are gentle on the stomach — useful when GI side-effects are already in play.
Only if you’re deficient
Iron
Low iron is a very common cause of tiredness — but only supplement if blood tests show you’re actually deficient. Too much iron is harmful, so this one is test-first, always.
Hydration
Electrolytes (sodium, potassium, magnesium)
Particularly helpful if you’re eating less, sweating during workouts, or drinking lots of water. Replacing electrolytes can ease the fatigue, headaches and cramps that come with under-eating.
Protect your muscle
Protein (the big one)
Not a supplement so much as a priority: when weight is dropping fast, adequate protein plus some resistance training is how you lose fat instead of muscle. Most people aim to hit protein first at every (smaller) meal.
