How to Calculate Macros for Fat Loss (Evidence-Based Guide)

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Getting Started

Cutting Through the Noise

There's no shortage of fat loss advice on the internet. Keto, carnivore, intermittent fasting, carb cycling, meal timing, "metabolic confusion". Everyone has a system, and they're all convinced theirs is the one that works.

Here's the thing: most of it is overcomplicating a straightforward process.

This guide walks you through how to correctly set your macros for a fat loss phase. No gimmicks, no tricks, no shortcuts. Just an evidence-based approach that's efficient and, importantly, safe. You'll understand exactly why each number is what it is, backed by research rather than influencer marketing.

Let's get into it.

Why Bodyweight Matters More Than Percentages

Most macro calculators use the classic 40/40/20 split (protein/carbs/fat). It's simple, but it has a fundamental flaw: your body doesn't care about percentages. It cares about absolute amounts relative to your size.

The 40% approach is a decent starting point for fat loss. At typical deficit calories, it usually lands in a reasonable range. But when you eventually transition to maintenance or a building phase, it breaks down completely. At 3,000+ calories, 40% protein becomes 300g+. That's expensive, hard to eat, and offers no additional benefit.

A bodyweight-anchored approach scales across all phases of your journey. Your protein stays tied to your actual tissue needs whether you're eating 1,600 or 3,500 calories.

Here's how to calculate it properly.

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Your Macro Targets

Protein: 2.0-2.2 g/kg of bodyweight

Here's something that surprises people: you need more protein during fat loss than during maintenance or building phases.

It seems backwards. Surely you need more protein when you're trying to grow? But during a deficit, your body is in a catabolic state. Higher protein intake protects muscle mass when your body is looking for energy to burn. During a surplus, adequate energy already supports an anabolic environment, so protein requirements are actually lower (1.8-2.0 g/kg).

Think of it as insurance: the more your body is under stress from dieting, the more protection your muscles need.

How to calculate:

• Multiply your weight in kg by 2.2
• Cap it at 40% of total calories or 2.6 g/kg (whichever is lower)
• Never reduce protein when cutting calories

Fat: 0.75 g/kg of bodyweight

Fat isn't just about calories. It's essential for hormone production and absorbing vitamins A, D, E, and K.

How to calculate:

• Multiply your weight in kg by 0.75
• Set a hard floor of 0.6 g/kg (never go below 15% of calories)
• This is what gets reduced first when you need to cut calories

Carbohydrates: Whatever remains

Carbs fuel your training and support recovery. They're the "flexible" macro during fat loss—adjusted based on what's left after protein and fat are set.

How to calculate:

• Take remaining calories after protein and fat
• Divide by 4 (calories per gram of carbs)
• Set a floor of 1.0 g/kg (1.5 g/kg if you train high-volume)

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Step-by-Step Calculation

Let's walk through an example: 75 kg person targeting 1,800 calories for fat loss.

Step 1: Protein

75 kg × 2.2 g/kg = 165g protein
165g × 4 calories = 660 calories

Check: 660 ÷ 1,800 = 37% (under 40% cap ✓)

Step 2: Fat

75 kg × 0.75 g/kg = 56g fat
56g × 9 calories = 504 calories

Check: 504 ÷ 1,800 = 28% (above 15% floor ✓)

Step 3: Carbs

Remaining: 1,800 - 660 - 504 = 636 calories
636 ÷ 4 = 159g carbs

Check floor: 75 kg × 1.0 = 75g minimum
159g > 75g ✓

Final Macros

Macro	Grams	Calories	%
Protein	165g	660	37%
Fat	56g	504	28%
Carbs	159g	636	35%

Notice how the percentages fall naturally from the bodyweight calculations, not the other way around.

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When You Hit a Plateau

Weight loss stalls. When it does, follow this priority order:

1. Increase Activity First

Add 1,000-2,000 steps before cutting food. Burn more, don't eat less.

2. Reduce Fat (If Needed)

• Calculate removable fat: (current fat - 0.6g/kg) × 9 calories
• Remove up to this amount first
• Never go below 0.6 g/kg or 15% of calories

3. Reduce Carbs (If Needed)

• Calculate removable carbs: (current carbs - 1.0g/kg) × 4 calories
• Remove up to this amount
• Never go below 1.0 g/kg

4. Protein Stays Constant

Never reduce protein. It's protecting your muscle mass.

Example Adjustment

Using our 75kg example, if you need to cut 200 calories:

Fat reduction: 56g - 45g = 11g × 9 = 99 calories removed Carb reduction: Remaining 101 calories ÷ 4 = 25g reduction

New macros: 165g protein, 45g fat, 134g carbs

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Want to understand the research behind these numbers? Keep reading.

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The Science

Protein: How Much Actually Preserves Muscle?

The International Society of Sports Nutrition recommends 1.4-2.0 g/kg for active individuals, noting that higher intakes are warranted during energy restriction [1].

A landmark 2016 study put this to the test. During a 40% calorie deficit with intense training, the group consuming 2.4 g/kg actually gained lean mass while losing more fat than the 1.2 g/kg group [2]. That's a substantial difference from the same calorie intake.

The most comprehensive guidelines for physique athletes recommend 2.3-3.1 g/kg of lean body mass during contest prep [3]. Since most people don't know their exact lean mass, using 2.0-2.2 g/kg of total bodyweight with a ceiling keeps you in the protective range without going overboard.

Fat: The Hormone Floor

A 2021 meta-analysis found that low-fat diets (~19% of calories) produced significant reductions in testosterone, free testosterone, and DHT compared to higher-fat diets (~39% of calories) [4]. The effect was particularly pronounced in men of European ancestry.

That said, overall energy availability matters more than fat intake alone. If you're in a large deficit, some hormonal suppression is likely regardless. The 0.6 g/kg floor (minimum 15% of calories) represents a balance: low enough to allow meaningful deficits, high enough to avoid unnecessary hormonal stress.

Carbs: Less Critical Than You'd Think

A 2022 systematic review found that in isocaloric conditions, carbohydrate intake had minimal impact on resistance training performance [5]. A typical one-hour session depletes only about 80g of glycogen—roughly 16% of what a trained athlete stores.

This doesn't mean carbs don't matter. They support recovery and help regulate hunger hormones. The 1.0 g/kg floor protects these functions while recognising that carbs are the most flexible lever during fat loss.

Rate of Loss: Why 0.5-1% Per Week

Research shows that weekly weight loss targets of 1 kg resulted in a 30% reduction in testosterone compared to 0.5 kg per week in resistance-trained athletes [3]. The more aggressive the deficit, the greater the hormonal disruption and muscle loss risk.

Targeting 0.5-1.0% of bodyweight per week is aggressive enough for meaningful progress, conservative enough to protect what you've built.

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References

1. Jäger R, et al. International Society of Sports Nutrition Position Stand: Protein and exercise. J Int Soc Sports Nutr. 2017;14:20.
   doi:10.1186/s12970-017-0177-8

2. Longland TM, et al. Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss. Am J Clin Nutr. 2016;103(3):738-746.
   doi:10.3945/ajcn.115.119339

3. Roberts BM, et al. Nutritional Recommendations for Physique Athletes. J Hum Kinet. 2020;71:79-108.
   doi:10.2478/hukin-2019-0096

4. Whittaker J, Wu K. Low-fat diets and testosterone in men: Systematic review and meta-analysis of intervention studies. J Steroid Biochem Mol Biol. 2021;210:105878.
   doi:10.1016/j.jsbmb.2021.105878

5. Henselmans M, et al. The Effect of Carbohydrate Intake on Strength and Resistance Training Performance: A Systematic Review. Nutrients. 2022;14(4):856.
   doi:10.3390/nu14040856

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Skip the Spreadsheets

This is exactly the methodology TrainingFuel implements automatically. We calculate your targets, monitor your progress, and adjust when things aren't working. No manual calculations or plateau guesswork required.