How Sleep Impacts Weightloss & Muscle Mass | Personal Training City of London
- John Pierson
- Apr 7
- 4 min read
Updated: Apr 8
As a personal trainer in the City of London, I work with professionals from a few industries: lawyers, bankers, and insurance workers.
And across all of them, one common theme stands out:
A disregard for personal health and fitness in favour of… The Firm.
Most people recognise the importance of exercise and nutrition as the cornerstones of good health. In many cases, workplaces even try to support this, as we see a growing emphasis on "work–life" balance.
But I’ve worked with enough of you to know there’s a genuine desire to improve
your health and fitness—and often, that motivation comes from trying to undo the toll that work takes.
Always on the go. Deprioritising yourself and pushing your body without enough recovery.
And then it’s 10:30 p.m., and you decide, “Just one last check of the emails…” — and there it is. The email that keeps you up all night, just in time for your 7 a.m. alarm.
But All Is Not Lost
There are things we can do to promote healthier sleep and reduce unnecessary muscle loss—even in a high-stress job.
Lack of Sleep Alters Fat Loss
A study published in the Annals of Internal Medicine confirmed what many of us have suspected: insufficient sleep can sabotage fat-loss goals.
Researchers studied 10 overweight but otherwise healthy adults on a calorie-restricted diet.
For two weeks, they followed the exact same diet under two different conditions:
8.5 hours of sleep per night
5.5 hours of sleep per night
The results were dramatic:
Results:
Sleep curtailment decreased the proportion of weight lost as fat by 55% (1.4 vs. 0.6 kg with 8.5 vs. 5.5 hours of sleep opportunity, respectively) and increased the loss of fat-free body mass by 60% (1.5 vs. 2.4 kg; P = 0.002). Markers of enhanced neuroendocrine adaptation to caloric restriction, increased hunger, and a shift in relative substrate utilisation toward less fat oxidation accompanied this.
I see this all the time with the professionals I train. It’s not just common—it’s expected. But these findings help us take action. They confirm what we feel and offer a framework for change.
Why Sleep Matters for Fat Loss and Muscle Maintenance
If you're trying to balance long hours with fitness goals, the quality and quantity of your sleep is just as important as your training and meal prep.
Here’s why sleep is essential:
Hormonal Regulation: Sleep influences hormones like leptin (signals fullness) and ghrelin (stimulates hunger). Less sleep = more cravings.
Muscle Preservation: Deep sleep is when your body repairs and builds muscle. Without it, your body taps into lean mass for energy.
Fat Oxidation: Reduced sleep shifts your metabolism from fat-burning to carb-burning—making fat loss harder.
The Cost of Cutting Sleep in the City
In the City of London, the fast-paced lifestyle leads to early starts, late dinners, and back-to-back meetings. You might be in the gym at 6 a.m. or squeezing in sessions where you can—but if you consistently get 5.5 hours of sleep, you’re working against your goals.
Sleep isn’t a luxury. It’s a performance enhancer, a fat-burning tool, and a muscle-preservation strategy.
Nutrition Tweaks That Help with Sleep & Recovery
Sleep and diet go hand in hand. Here are two things that can make a real difference:
Carbohydrates
Lots of people cut carbs when trying to lose weight. While that can be effective, it’s not always necessary. Eating carbohydrates before bed has been shown to improve both sleep quality and quantity. So if you’re on a low-carb diet and struggling to sleep—this might be worth revisiting.
Protein
Upping your protein intake can help protect muscle during fat loss. Aim for 1.2–2 grams of protein per kilo of bodyweight.If you weigh 80kg, that’s up to 160g per day—high, but beneficial, especially if you’re in a calorie deficit.
How to Improve Your Sleep
I’m not a sleep scientist—but I’ve been sleeping my whole life, so I’ve picked up a few things. The first step? Read Why We Sleep by Matthew Walker.
Here are 3 simple, research-backed tips from his work:
1. Stick to a Consistent Sleep Schedule
“The brain has a hardwired need for regularity.”
Wake up and go to bed at the same time—even on weekends.
2. Cool Down Your Room
“Your body needs to drop its core temperature by about 1°C to initiate sleep.”
Aim for a room temperature around 18°C.
3. Cut the Caffeine & Alcohol
“Caffeine blocks adenosine, the chemical that helps you feel sleepy.”
Limit caffeine after 2 p.m. and avoid alcohol close to bedtime.
So Boring It Sent You to Sleep?
It’s not the flashiest topic, but hopefully, this post has made you think beyond training volume and calorie targets. The City is a demanding place, and recovery trends are getting more extreme but nothing competes with the recovery system your body already has: sleep.
As your trainer, I’m here to help you succeed in every area of your health. That includes reminding you that
your best recovery tool costs nothing—it’s sleep.
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