What Happens When You Consistently Under-eat?
We’re talking about nutrition, and we’re starting with something that might surprise you.
Most diets work the same way. Restrict hard. Rely on willpower. White-knuckle through hunger until you eventually crack.
GLP-1 medication flips this. Appetite disappears. Willpower isn’t the problem anymore.
You’re not fighting the urge to eat; you’re forgetting to eat entirely.
That sounds like a win. Short term, yes.
Long term, not so much.
When appetite tanks, people stop eating. Not strategically. Not in a controlled deficit. They go from three meals to one. Maybe a snack. Some days, almost nothing.
You’re not hungry, so it doesn’t feel like a problem.
But it is.
What happens when you consistently under-eat:
You lose muscle, not just fat.
Your body needs protein and energy to maintain muscle tissue. When intake drops too low, your body will eventually start breaking down muscle for fuel. The number on the scale drops, but you’re losing the wrong kind of weight. (More on protecting muscle in [Why Strength Training Matters More Now].)
Your metabolism slows.
Less muscle means a slower metabolic rate. This makes it harder to maintain your results when appetite returns – due to dose changes, adaptation, or reduced medication.
Energy crashes.
Even if you feel fine for a while, chronic under-eating catches up with you. Fatigue, brain fog, irritability–these aren’t signs of discipline. There are signs your body is running on empty.
Recovery suffers.
If you’re strength training (and you should be), your body needs fuel to repair and adapt. Under-eat, and you don’t get the benefits of the work you’re putting in.
Hair starts thinning. Nails go brittle. Skin dries out.
One of the most common complaints about GLP-1s. Often blamed on the medication, but usually caused by inadequate nutrition. Your body prioritises vital functions — cosmetic stuff gets cut first.
When liquid calories make sense:
Normally, I push whole foods. Chewing, volume, and satiety–all useful when appetite is normal.
But when appetite tanks, whole foods can feel impossible. This is where calorie-dense shakes bridge the gap. Oats, peanut butter, banana, milk, protein powder; blended into something you can drink when you can’t face eating.
Not a daily crutch. A strategic tool for the days when solid food isn’t happening.
The reframe:
Eating to train is not the same as overeating. Fuelling your body to protect muscle, support recovery, and maintain energy isn’t going backwards. It’s the whole point.
The medication makes eating less easier. That’s the point. But “less” doesn’t mean “barely surviving.”
You still need a baseline of calories and protein, even when hunger is low.
Not skipping meals entirely, even if portions are small.
Prioritising protein at every meal.
Eating something, even when you’re not hungry.
This isn’t about forcing food down. It’s about making sure the weight you lose is fat, not muscle — and that you’re not setting yourself up for problems later.
Next: [Protein – The Non-Negotiable]
Why it matters more now than ever, and how much you actually need.