Most people who start paying attention to their diet focus on one number: calories. And calories do matter — a calorie surplus causes fat gain, a calorie deficit causes fat loss, full stop. But here’s what I discovered after months of hitting my calorie target and still not getting the body composition results I wanted: how you fill those calories matters just as much as the total.
Once I started tracking macros alongside calories, everything changed. I held on to more muscle during my fat loss phase, I performed better in the gym, and I felt noticeably fuller on the same number of calories. This is the part of the James Smith approach that often gets overlooked. He doesn’t just tell you how many calories to eat — he tells you how to structure them.
What Are Macros?
Macros, short for macronutrients, are the three main categories of nutrients that provide energy:
- Protein — 4 kcal per gram. Builds and repairs muscle tissue, keeps you full through satiety hormones, and has the highest thermic effect of feeding — meaning your body burns more energy digesting it than any other macro (roughly 20–30% of protein calories are burned in digestion). Think chicken breast, eggs, Greek yoghurt, fish, tofu, legumes.
- Carbohydrates — 4 kcal per gram. Your body’s preferred fuel source, especially for high-intensity training. Think rice, oats, bread, potatoes, fruit. Contrary to popular belief, carbs do not cause fat gain — excess calories do.
- Fats — 9 kcal per gram. Essential for hormone production (including testosterone and oestrogen), brain function, joint health, and absorbing fat-soluble vitamins A, D, E and K. Think olive oil, avocado, fatty fish, nuts, dairy.
When you know your total daily calorie target, macros tell you how to fill those calories in a way that supports your goal — not just your weight on the scale, but your actual body composition: the ratio of fat to muscle tissue.
James Smith’s Protein-First Philosophy
The foundation of the James Smith macro approach is simple: calculate protein first, set fats at a healthy fixed percentage, and fill the rest with carbohydrates. This ordering is deliberate and important.
Protein is set at 2 g per kg of bodyweight. This might sound high compared to older nutritional guidance suggesting 0.8 g per kg — but that figure was based on the minimum needed to avoid deficiency, not the amount needed to preserve or build muscle while in a calorie deficit.
Research from the British Nutrition Foundation and multiple sports science studies consistently supports higher protein intakes of 1.6–2.2 g per kg for individuals engaged in resistance training, particularly during calorie restriction. At 2 g per kg, you are well within the range shown to maximise muscle protein synthesis and preserve lean mass during a diet.
The reason this matters: when you are in a calorie deficit, your body needs a clear signal to preserve muscle tissue. Adequate protein combined with resistance training sends that signal. Without enough protein, your body is far more likely to break down muscle for fuel alongside fat — meaning you end up lighter on the scale but with a worse body composition than when you started. This is known as “skinny fat” — lighter but less defined.
A Worked Example
If you read my previous post on how to start with your TDEE calculation, you’ll remember Alex: a 30-year-old male, 80 kg, 178 cm, moderately active, with a fat loss calorie target of 2,286 kcal per day (a 20% deficit from his 2,858 kcal TDEE). Here is exactly how we split those macros.
Step 1 — Protein
2 g × 80 kg = 160 g protein per day
160 g × 4 kcal/g = 640 kcal from protein
Step 2 — Fats
25% of total daily calories = 0.25 × 2,286 = 571.5 kcal from fat
571.5 ÷ 9 kcal/g = 64 g fat per day (576 kcal)
Step 3 — Carbohydrates (the remainder)
Remaining calories = 2,286 − 640 (protein) − 576 (fat) = 1,070 kcal
1,070 ÷ 4 kcal/g = 268 g carbohydrates per day
Alex’s full daily macro targets:
- Protein: 160 g (640 kcal)
- Fats: 64 g (576 kcal)
- Carbs: 268 g (1,072 kcal)
- Total: approximately 2,288 kcal
To put those numbers into real food terms: 160 g of protein is roughly the equivalent of four chicken breasts spread across a full day of meals. 268 g of carbs is comfortably achievable with oats at breakfast, rice at lunch, and potatoes or pasta at dinner. 64 g of fat covers cooking oil, some dairy at breakfast, and a handful of nuts as a snack.
These are targets, not a rigid prescription. The goal is to land close to these numbers across the week, not to hit them precisely every single day.
The Carbs Myth
One thing I want to address directly because I hear it constantly: carbohydrates do not cause fat gain. Fat gain comes from a sustained calorie surplus — consuming more total energy than your body uses over time. Carbs eaten within your calorie target will not make you gain fat, regardless of how many grams they represent.
Low-carb diets work for some people because reducing carbs often naturally reduces total calorie intake, and because glycogen (stored carbohydrate) holds water in a roughly 3:1 ratio. So the rapid weight loss people see in the first week of a low-carb diet is largely water, not fat. The same calorie deficit achieved with moderate carbohydrates produces the same rate of fat loss over time.
Carbohydrates are particularly valuable if you train. They fuel performance, preserve muscle glycogen, and help you feel energised and motivated in sessions. Aggressively cutting carbs while training hard is one of the most common reasons people feel weak, flat, and mentally foggy after two or three weeks of a diet. Protein and fat can’t fully substitute for carbohydrates as a fuel source for high-intensity work.
Why Tracking Macros Beats Just Counting Calories
Two people can eat the same number of calories and end up with very different body compositions over time. Person A eats 2,000 kcal mostly from processed carbohydrates and fats with very little protein. Person B eats 2,000 kcal split across 160 g protein, 220 g carbs and 55 g fat. After 12 weeks in a deficit, Person B will likely have retained significantly more muscle — despite an identical calorie deficit.
Body composition is the goal, not just the number on the scale. The scale is a blunt instrument that combines fat, muscle, water, bone density and food volume. Tracking macros — particularly hitting your protein target — is what determines the quality of the weight you lose.
When I started prioritising protein, I noticed the difference within about six weeks. I was losing a similar amount of scale weight as before, but I looked noticeably more defined — because I was losing fat while preserving muscle, rather than losing both indiscriminately.
Get Your Macro Targets Instantly
You do not need to do this maths yourself every time. The James Smith Calculator I built does all of this automatically in about 90 seconds — just enter your stats and goal, and it outputs your exact protein, carb and fat targets.
Try the James Smith Calculator →
Recalculate Every 4–6 Weeks
As your weight changes, so do your macro targets. Protein is based on bodyweight — if you drop from 80 kg to 74 kg over the course of 12 weeks, your protein target drops from 160 g to 148 g, and your overall calorie target decreases because a lighter body burns fewer calories at rest and during activity.
Most people set their macros once at the start of a diet and never update them. This is one of the main reasons progress stalls after the first couple of months — the targets are no longer accurate for the body they have now. Recalculate every 4–6 weeks, or any time your weight changes by more than 3–5 kg.
Also read: how to set the right calorie deficit for your goal — including when to increase or reduce your deficit based on actual results over 2 weeks of consistent tracking.
Macros are a guide, not a rigid prescription. Adjust based on how you feel, how you are performing in training, and what your actual results show over time. This post is based on personal experience adjusting macros across multiple fat loss and muscle gain phases. It is not medical advice — consult a healthcare professional if you have specific dietary requirements or health conditions.