The short version
- Starting point: your body weight in pounds multiplied by 13 to 14.
- Go lower and you're more likely to run low, eat to treat it, and under-recover.
- Go higher and you need more insulin to cover the food, which works against fat loss.
- Start at 13.5, track your trend for two to three weeks, then adjust.
One note before the detail. This is how I think about it as a coach who has type 1. It isn't medical advice. Your diabetes team stays in charge of your insulin, so agree any change to doses with them.
The formula
Take your body weight in pounds and multiply it by 13 to 14. That's your daily calorie target for fat loss.
For someone who weighs 170 lb and trains four times a week, that's roughly 2,200 to 2,400 calories a day.
Why not go lower?
A generic calculator set up for a hard cut might tell that same person to multiply by 10 or 11. That's around 1,700 to 1,900 calories. Without type 1, that's tough but workable.
With type 1, it tends to go wrong in three ways:
- More lows. You're more likely to run low during or after training. You treat it, and you've added back 200 or 300 calories you didn't plan for.
- Worse recovery. You're under-fuelled for the sessions you're doing.
- More hunger. Eating too little for too long raises stress hormones like cortisol, and they make you hungrier.
So you end up doing the hardest version of the diet and getting the slowest results from it.
Sports science calls the bigger issue energy availability. Think of calories as fuel in a car. Training burns some. What's left is what your body runs everything else on: hormones, sleep, recovery. Cut too low for too long and there's nothing left for any of that.
Why not go higher?
If you eat more than you need, you need more insulin to cover it. Insulin builds things up, including fat. So you end up working against yourself from the other direction.
There's a quieter version of this too. A sauce here, a few extra carbs "to be safe" before training, a bigger hypo treatment than you needed. None of it is a character flaw. It's just untracked.
How to find your number
- Start in the middle, at body weight times 13.5.
- Track your trend for two to three weeks. One day's weight tells you very little.
- If lows are frequent, nudge towards 14.
- If your trend is flat after three weeks, nudge towards 13.
You're adjusting from real signals from your own body. That only works if you're tracking honestly.
What to put inside the number
- Protein: around 1 gram per pound of body weight, spread over two to four meals. It protects muscle in a deficit and it's the most filling thing you can eat.
- Carbs: more of them around training, before and after, when you need the fuel. Fewer on rest days, with a bit more fat to fill the gap.
- Fibre: it slows digestion and helps flatten your blood sugar response to a meal. Lean protein, vegetables and a measured carb portion give you a much gentler curve than the same calories from something more refined.
What a day can look like
- Breakfast with protein and a moderate carb portion
- A small carb snack before training
- Your biggest meal after training, with more protein and carbs
- Dinner a little lighter in carbs, built around protein, vegetables and fat
It doesn't need to be exact. It needs to be consistent enough that your three-week trend means something. The number that works is usually less dramatic than people expect, and far easier to keep going with.