How lack of sleep can affect your weight loss journey

It’s 3am and you’re doing maths in the dark.

Fourteen weeks into your new plan. Half your dinner left on the plate most nights. And this month the scale has moved exactly nowhere.

What the heck is happening?

Meet Jen. She has come on seven retreats with me, and twelve months ago her doctor prescribed a GLP-1 medication.

Life had thrown the lot at her. A divorce. The death of her mum. An empty nest. Menopause on top of it all. And her blood tests showed the chaos.

Her cardiologist went through her fasting insulin, a sluggish thyroid, climbing cholesterol and the odd episode of atrial fibrillation, which is an irregular heartbeat. Her medication was one part of a wider plan.

For a while, things went to plan.

Then her dad went into aged care and the insomnia took hold. For four months Jen averaged five and a half hours of sleep a night, at most.

Five to six hours. Hold that number. We’re coming back to it.

Before we get to the science, hear this. You have not failed. A GLP-1 plateau happens to plenty of people on GLP-1 medications, and it usually has very little to do with willpower.

So put down the stick you’ve been beating yourself with. We’re going to look somewhere far more interesting. Your bedroom.

Okay, not like that.

What your medication can’t do

GLP-1 medications work on appetite. How they fit into your treatment is a conversation for you and your prescriber.

But a medication can’t tuck you in. It can’t answer the 9pm email from your boss, settle your nervous system, or take the phone out of your hand at midnight.

And that matters more than most people are ever told. Sleep and stress have their own say over hunger, cravings and how easily your body lets go of fat. If they’re pulling one way while your medication pulls the other, you can do everything right and still stand still.

Same diet, different pillow

Here’s a study that deserves a spot on every fridge.

Researchers at the University of Chicago put a small group of adults on the same reduced-calorie diet, twice. One round they got 8.5 hours in bed. The other round, 5.5.

Jen’s number, give or take.

They lost about the same weight both times. But on short sleep, 55 per cent less of that weight was fat, and they lost 60 per cent more lean tissue. Lean tissue includes muscle, the very thing we’re working so hard to protect on these medications.

Same food. Same people. Less sleep.

It was a small study, ten people over two weeks, so we hold it lightly. But it lines up with a bigger one. When another Chicago team helped 80 short sleepers get just over an extra hour a night, they ate about 270 fewer calories a day. Nobody handed them a diet. They slept more and wanted less.

It’s science, not fiction.

Tired but wired: where stress comes in

Now add stress.

You know the feeling. Flat all day, then your head hits the pillow and your brain opens seventeen tabs. Tired but wired.

That’s cortisol, your main stress hormone, staying on duty when it should have clocked off. A bit of it is useful. It gets you out of bed and through a deadline. The trouble starts when it never goes home.

When researchers followed 339 adults for six months, the ones who started out with higher cortisol and more chronic stress gained more weight. A hunger hormone called ghrelin predicted more food cravings.

Stress and sleep also feed each other. A bad night makes tomorrow harder. A hard day makes tonight worse. And so it loops.

You can be doing everything your doctor asked and still have a body that thinks it’s under siege.

I call stress the waistline stowaway. It sneaks on board through a completely different door to food, and no meal plan will find it.

The twist nobody mentions: eating less can cost you sleep

When your appetite drops, so does everything that arrives with food. That includes the nutrients that help you rest.

A 2025 study looked at three days of food diaries from 69 people on GLP-1 medications. On average they fell short on magnesium, calcium, iron, potassium and a handful of vitamins. Protein was low too, once body weight was taken into account.

Magnesium has a hand in muscle relaxation and a calm nervous system. Am I telling you a supplement will fix your plateau? I believe there is a time and a place for supplements but food is always the first choice.

If you’re eating half of what you used to, every mouthful has to work harder.

Nourish, not punish.

Science Says

How much is enough? An expert panel convened by the US National Sleep Foundation recommends seven to nine hours a night for adults aged 18 to 64, and seven to eight hours for those aged 65 and over.

Source: Hirshkowitz and colleagues, Sleep Health, 2015.

Seven micro habits to try tonight

Pick one. Not seven. You’re tired enough.

1.     Give yourself a bedtime. Kids get one for a reason. Choose a lights-out time that allows seven to eight hours and guard it like a table at your favourite restaurant.

2.     Get outside in the morning. A short walk, a coffee on the back step. Morning light helps set your body clock, so sleep comes easier that night.

3.     Put protein on your breakfast plate. Eggs, Greek yoghurt, cottage cheese, last night’s salmon. It steadies your energy so you’re not running on fumes by 3pm.

4.     Eat your magnesium. Pumpkin seeds, almonds, spinach, black beans. And yes, a square of dark chocolate. You’re welcome.

5.     Coffee before noon. Caffeine hangs around for hours. Your 3pm flat white is still at the party at 10pm.

6.     Mind the wine. I wrote a book with the word “drink” in the title, so I’m not coming for your glass of red. Just know that alcohol helps you nod off, then breaks up your sleep in the second half of the night. Earlier and less is kinder.

7.     Walk to calm down, lift to hold on. A walk you enjoy settles your system. Strength work twice a week helps protect the muscle that short sleep likes to steal.

So what happened to Jen?

Remember Jen, and her five to six hours?

We went after her sleep. Three changes, none of them glamorous.

1.     Magnesium glycinate, 90 minutes before bed. Yes, I said food first. Jen checked with her doctor before adding a supplement, and it was one piece of a bedtime routine, not the hero.

2.     The nightly glass of red went. I know, I said I wasn’t coming for your wine. But Jen’s was every night, and sleep was her problem. We swapped it for a caffeine-free rooibos tea, sipped in a warm Epsom salt bath. Does the magnesium soak in through your skin? The science isn’t convinced. A warm bath and a quiet cuppa are still a lovely way to tell a wired body the day is done.

3.     A support group. Jen joined a group for people with elderly parents, run at her father’s dementia care facility. Because the stress keeping her awake was never about food.

Jen worked her way back to her normal eight hours a night.

Her weight settled where she and her doctor wanted it.

And those chaotic blood tests? Her latest results were a big improvement, with her whole care team behind that, not just a bedtime. Everyone is different, and your results will be too.

Same Jen. Two to three more hours of sleep a night.

When to call your doctor

If your partner says you snore like a freight train, if you wake up gasping, or if you’re wrecked no matter how long you sleep, ask your GP about sleep apnoea. It’s common and it’s treatable.

And please don’t change your dose, skip injections or start supplements without talking to your prescriber first. Work with a nutritionist who supports your physical, emotional and mental wellbeing. That’s what we are here for.

The bit to remember

A plateau doesn’t mean you’re broken, and it isn’t a sign to change anything about your treatment without your prescriber. Sometimes your body is asking for something no injection can deliver. Rest.

So tonight, skip the 3am maths. Leave the phone in the kitchen, get under the doona like it’s an appointment you can’t miss, and let your body do its quiet work.

You’ve got a life to enjoy. Go to bed.

Quick questions

Can stress cause a weight loss plateau?

It can play a part. Chronic stress and higher cortisol have been linked with weight gain over time, and stress tends to wreck sleep as well. Both can slow progress, whatever else you’re doing.

Does poor sleep affect weight loss?

The studies so far were done in people who were dieting, not people on GLP-1 medications. In those studies, short sleep meant less fat lost, more lean tissue lost and a bigger appetite. That’s reason enough to protect your sleep.

How much sleep do I need while I’m losing weight?

Most adults do best on seven to nine hours. If you’re regularly under six, start there before you change anything else.

This article is general information, not personal medical advice. Talk to your GP or prescriber about your own situation.

References

1.     Nedeltcheva AV, Kilkus JM, Imperial J, Schoeller DA, Penev PD. Insufficient sleep undermines dietary efforts to reduce adiposity. Annals of Internal Medicine, 2010.

2.     Tasali E, Wroblewski K, Kahn E, Kilkus J, Schoeller DA. Effect of Sleep Extension on Objectively Assessed Energy Intake Among Adults With Overweight in Real-life Settings: A Randomized Clinical Trial. JAMA Internal Medicine, 2022.

3.     Chao AM, Jastreboff AM, White MA, Grilo CM, Sinha R. Stress, cortisol, and other appetite-related hormones: Prospective prediction of 6-month changes in food cravings and weight. Obesity, 2017.

4.     Johnson B, Milstead M, Thomas O, McGlasson T, Green L, Kreider R, Jones R. Investigating nutrient intake during use of glucagon-like peptide-1 receptor agonist: a cross-sectional study. Frontiers in Nutrition, 2025.

5.     Mah J, Pitre T. Oral magnesium supplementation for insomnia in older adults: a Systematic Review & Meta-Analysis. BMC Complementary Medicine and Therapies, 2021.

6.     Ebrahim IO, Shapiro CM, and colleagues. Alcohol and Sleep I: Effects on Normal Sleep. Alcoholism: Clinical and Experimental Research, 2013.

7.     Hirshkowitz M, Whiton K, Albert SM, and colleagues. National Sleep Foundation’s sleep time duration recommendations: methodology and results summary. Sleep Health, 2015.

Gröber U, Werner T, Vormann J, Kisters K. Myth or Reality: Transdermal Magnesium? Nutrients, 2017.