How to Lose 5KG in 10 Weeks and Get Faster

Matt breaks down how to safely lose 5kg+ during a marathon block — using calorie deficits on easy days and big carb windows around hard sessions — so you can train hard and run faster.

Matt Fox / Sweat Elite

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Matt talks about how to lose five kilograms or more in the ten weeks leading into a marathon — while still training hard and aiming to run faster. He pushes back on the old idea that you should finish all weight loss before the marathon-specific block, and shares how he’s used this approach five times himself, including a recent stretch where he dropped nearly fifteen kilos.

Matt walks through the method in plain terms: stay in a calorie deficit most of the week, track burn with a watch or rough math, log food with AI photo counting, and then flip into big carbohydrate windows around your two hardest sessions so quality workouts don’t suffer. He lands on roughly an eight-hundred-calorie deficit on easy days — enough, on paper, to lose about half a kilo a week and five kilos over ten weeks.

Matt is clear this is not for everyone. If you’ve dealt with an eating disorder, RED-S, or low energy availability — or you’re already below a healthy weight — he says turn the episode off. For listeners who can safely lose the weight, he also covers strength work, bone-health basics, and where coaching or a meal plan fits if you want more accountability.

Timestamps
00:01 Content warning & who should skip
00:36 The goal
02:20 The only rule that matters
03:43 How to track burn
05:33 How to track intake
06:11 Weekly structure: deficit + carb windows
08:00 Hard-session fueling
11:03 Easy-day eating
13:19 GLP-1 note (personal, not recommended)
14:55 The math (why ~800/day)
16:16 Injury-risk buffers
17:45 Risk framing
19:10 Coaching / meal plans
Content warning & who should skip

Eating disorders, RED-S, LEA, and already-lean athletes should not follow this advice. Aimed at people who can safely lose ~5kg+ and want to run faster.

The goal

Lose 5kg+ in the ~10-week marathon-specific block; Matt’s personal and coaching experience; pushback on “never diet in the marathon block.”

The only rule that matters

Calorie deficit = burn more than you eat. Tracking makes it workable; perfection isn’t required.

How to track burn

Garmin (or similar) preferred. Rough guide: ~2,000 kcal/day for many men (5–7k steps); ~1,700 for many women; easy running ~700 kcal/hour; hard running closer to ~1,100 kcal/hour.

How to track intake

Photo-log every meal/drink in ChatGPT (or similar AI); build one daily log; close enough beats exact.

Weekly structure: deficit + carb windows

Most of the week (~5.5 days): solid deficit (~800 kcal/day as a working target).
Around 2 hard sessions (e.g. Wed + Sun): stop deficit counting ~12 hours before; load carbs heavily before, during, and a few hours after.

Hard-session fueling

Example carb load ~400g in the pre-session window; in-session carbs often 70–100g/hour for men (women slightly lower); prioritize white rice, potatoes, bread, pasta in those windows.

Easy-day eating

High-volume, low-calorie foods (fruit, veg, lean protein); flavored soda water as a hunger/dopamine hack; ask AI for satiating low-cal meal ideas.

The math (why ~800/day)

~7,700 kcal deficit ≈ 1kg fat; ~3,800/week ≈ 0.5kg/week ≈ 5kg in 10 weeks. Surpluses in carb windows are expected; the weekly total still lands if easy days stay consistent.

Injury-risk buffers

Start strength (esp. squats) ~1 month before dieting; Vitamin K2 + calcium; prefer food calcium (eggs, milk, cheese). Don’t stack diet + big training jump + new gym all at once.

GLP-1 note (personal, not recommended)

Matt mentions microdosing; does not recommend listeners do the same; notes possible GI issues with late-run carbs and plans to stop near race day.

Risk framing

Acknowledges risk; argues high volume is often riskier than a controlled 5kg loss in a block, based on his experience and listener feedback.

Coaching / meal plans

Nutrition coaching (daily accountability) and one-off marathon meal plans available via the link in the episode description.

Key takeaways
Deficit most days; carb-load hard sessions hard
Track burn + intake closely enough to hit ~0.5kg/week
Protect bones and quality sessions; don’t copy medical shortcuts casually
Skip this entirely if ED / RED-S / LEA history or already underweight