How do you calculate macros for a client?

Step 1: the energy target

Macros are a way of dividing up an energy target, so get that right first. Estimate resting energy with a BMR equation, multiply by an activity factor to get maintenance, then take away energy for weight loss or add it for weight gain. Which BMR formula to use covers the first part.

For fat loss, a deficit that produces 0.5 to 1% of body weight a week is a sensible range for most adults. A kilogram of body mass is worth roughly 7700 kcal, so losing 0.5 kg a week needs a daily deficit of about 550 kcal.

Then protein, fat and carbs, in that order

Protein (g) = body weight (kg) × g/kg
Fat (g)     = energy target × fat % ÷ 9
Carbs (g)   = (energy target − protein g × 4 − fat g × 9) ÷ 4

• Protein in grams per kilogram. 1.2 to 1.6 g/kg suits most adults who are losing weight or training, and up to about 2.2 g/kg for lean clients in a hard deficit. How to work out protein needs goes through the ranges.
• Fat as a share of energy. 25 to 35% is typical. Going below 20% for long makes it hard to meet essential fatty acid needs and absorb fat-soluble vitamins, and most clients find it hard to stick to.
• Carbohydrate gets the rest. Training volume is the main reason to push it higher. Clients who prefer lower-carb eating can move energy from carbs to fat once protein is set.

Why protein first? A fixed percentage ties protein to calories. A client on 1500 kcal with 25% protein gets 94 g, and a client on 3500 kcal gets 219 g. Neither matches what their body needs, which depends on size and lean mass, not on how much they eat.

A worked example for weight loss

Your client is a 38-year-old woman, 72 kg and 165 cm, with a desk job and three gym sessions a week. Mifflin-St Jeor gives a resting energy expenditure (REE) of about 1403 kcal, and a PAL of 1.76 puts maintenance at about 2469 kcal. She wants to reach 65 kg, and at 0.75% of body weight a week (0.54 kg) the deficit is about 594 kcal a day.

Energy target = 2469 − 594         = 1875 kcal
Protein       = 72 × 1.6           = 115 g  (460 kcal)
Fat           = 1875 × 0.30 ÷ 9    = 63 g   (567 kcal)
Carbs         = (1875 − 460 − 567) ÷ 4 = 212 g (848 kcal)

Split: 25% protein, 30% fat, 45% carbohydrate

In kilojoules, that's a target of about 7850 kJ. Check the split against the Acceptable Macronutrient Distribution Ranges below. Hers sits inside all three.

Guard rails

These ranges come from the US Institute of Medicine and describe intakes linked with lower chronic disease risk in the general population. Athletes and clients in a steep deficit often sit outside them on purpose, usually with more protein and less carbohydrate. That's fine when you can say why.

Don't let a low energy target squeeze everything. There isn't a single minimum calorie intake that applies to every adult; energy prescriptions should be individualised while maintaining nutritional adequacy. As energy intake becomes increasingly restricted, meeting nutrient requirements can become more difficult. NICE defines 800–1,200 kcal/day as a low-energy diet and <800 kcal/day as a very-low-energy diet and recommends that these approaches are nutritionally complete, time-limited and delivered with appropriate clinical support and supervision.

Monitor weight and progress towards the agreed goal regularly. Assess the overall weight trend over several weeks rather than reacting to individual weigh-ins. If progress is broadly in line with the agreed goal, there may be no need to adjust the plan. If progress consistently differs from expectations, review adherence, dietary intake and activity before adjusting the energy prescription. Any calorie adjustment should be individualised while maintaining adequate protein and overall nutritional adequacy.