Calories tell you how much energy is on the plate. Macros — protein, carbohydrate, and fat — tell you what that energy is made of. You can lose weight on almost any split of the three, which is why arguments about “low carb” and “low fat” go on forever. You cannot train well, stay full, or keep muscle on a split that ignores protein and pushes fat so low that meals become sad.
Once you have a calorie target you can live with, macros are just a way of spending it. Set protein first, give fat a sensible floor, and let carbohydrate fill what is left. Then stop tinkering for a month.
The only arithmetic you need
Protein and carbohydrate provide about 4 kilocalories per gram. Fat provides about 9. Alcohol, which people forget to log, is about 7 per gram and does not become muscle. If a label says 20 grams of protein, that is roughly 80 kilocalories from protein, whether the food is chicken or yoghurt.
UK packets show energy in both kilojoules and kilocalories, usually per 100 grams and per portion. Trust per 100 grams when the “portion” is optimistic. A third of a sharing bag is still a third of the bag, not the 30 gram suggestion printed near the barcode.
Protein first
If you lift weights, a useful daily range is about 1.6 to 2.2 grams of protein per kilogram of body weight. You do not need to live at the top of that range. The middle is plenty for most people. Someone who weighs 80 kilograms and picks 1.8 grams per kilogram is aiming at about 145 grams of protein, which is about 580 kilocalories.
Spread it across the day. Breakfast is where most British diets fall short: cereal and milk can be enough, but toast and jam will not get you there. Eggs, Greek yoghurt, milk, tofu, fish, lean meat, and a scoop of protein powder are all legitimate. Powder is a convenience, not a moral category. Whole foods still bring iron, and in the case of dairy, calcium.
If you are in a calorie deficit, protein earns its place twice. It costs more energy to digest than carbohydrate or fat, and it protects the muscle you are training to keep. It is also the macro most likely to make a 500-kilocalorie dinner feel like dinner.
Do not push fat through the floor
Fat carries flavour, keeps hormones on an even keel, and helps you absorb some vitamins. A practical floor for most adults is around 0.6 to 1 gram per kilogram of body weight. For that same 80 kilogram person, 0.8 grams per kilogram is 64 grams of fat, about 575 kilocalories. Olive oil, nuts, eggs, dairy, and oily fish cover it quickly. You do not need to drink oil, and you do not need to ban butter from a roast potato.
Very low-fat diets tend to fail in ordinary kitchens because the food stops tasting like food. Very high-fat diets, inside a tight calorie target, squeeze out the carbohydrate that makes training feel possible. Neither extreme is required.
Carbohydrate is the remainder, and it is not the villain
Subtract protein and fat calories from the daily target. What is left, divided by 4, is your carbohydrate budget in grams.
Here is one illustration, not a prescription. An 80 kilogram person with a 2,400 kilocalorie target, 145 grams of protein (580 kilocalories) and 64 grams of fat (575 kilocalories) has about 1,245 kilocalories left. That is roughly 310 grams of carbohydrate. Rice, potatoes, fruit, oats, and bread are how you spend it, especially in the meals around training. On a rest day you can shift some of that toward extra vegetables and still hit protein. You do not need a separate identity as a “high carb” or “low carb” person.
Fibre sits inside the carbohydrate number on a UK label. Most adults do better with something in the region of 30 grams of fibre a day, from veg, fruit, pulses, and whole grains. If you raise fibre quickly, do it over a week or two and drink water with it. A sudden bowl of bran is a memorable mistake.
Training days and rest days
You can eat the same targets every day. That is simpler, and simple wins. If you prefer a rhythm, move 150 to 250 kilocalories of carbohydrate from a rest day onto a training day and keep the weekly total the same. The session gets more fuel. The week does not secretly grow.
Meal timing matters less than people hope. Eating protein across three or four meals is enough. A meal in the two or three hours before training, and something with protein and carbohydrate afterwards, covers the practical case. You will not lose the session because dinner was at 8pm instead of 7.
How close is close enough?
Hit calories within about 100 kilocalories on most days, and protein within about 15 grams. Chasing carbohydrate to the exact gram is how logging becomes a second job. Restaurant meals, homemade stews, and anything described as “a drizzle” are estimates. Log the best match, round slightly up if you are unsure, and eat the meal in peace.
If the scale trend and the gym log disagree with the diary — weight rising while you swear you are under, or strength collapsing while you swear you are eating enough — believe the trend. The diary has a hole in it. Find the hole (cooking oil, weekend drinks, bites while cooking) before you cut the target again.
In the app. SimplyAI shows calories, protein, carbohydrate, and fat against one daily target, from a photo, a barcode, or a search. Set the targets with the method above, then let the app keep score. It will not decide whether the split suits your training. You still have to.