IIFYM: The Complete Beginner's Guide to Flexible Dieting in 2026

You’ve seen it in fitness communities: someone posts a photo of pizza and ice cream, claims they’re on a “diet,” and tags it #IIFYM. It sounds too good to be true.

It’s not. But it’s also more nuanced than “eat whatever you want.” Here’s everything you need to know about If It Fits Your Macros — the flexible dieting approach that’s taken over the fitness world.

What Is IIFYM?

IIFYM stands for If It Fits Your Macros. It’s a flexible approach to dieting where you can eat any food you want, as long as it fits within your daily macronutrient targets.

Instead of following a rigid meal plan (“eat 200g chicken breast with 150g brown rice at 12:30pm”), you set daily targets for:

• Protein (in grams)
• Carbohydrates (in grams)
• Fats (in grams)

Then you fill those numbers however you like. Want pizza for lunch? Fine — adjust your other meals to hit your targets. Fancy a chocolate bar? No problem, as long as the macros work.

The core principle: your body doesn’t care whether protein comes from chicken or lentils. What matters is hitting the right amounts of each macronutrient.

Why IIFYM Works (The Science)

IIFYM isn’t just bro-science. Multiple studies have shown that macro composition — not specific food choices — is the primary driver of body composition changes.

Key findings:

• A 2020 meta-analysis in the Journal of the International Society of Sports Nutrition found no significant difference in fat loss between flexible and rigid dieting approaches when macros were matched
• Research consistently shows that dietary adherence is the strongest predictor of success — and flexible diets have significantly higher adherence rates
• Protein intake (not protein source) is the primary determinant of muscle retention during fat loss

The takeaway: the best diet is the one you can actually stick to. IIFYM works because it doesn’t require you to eat foods you hate or avoid foods you love.

How to Calculate Your IIFYM Macros

Step 1: Calculate Your TDEE

Your Total Daily Energy Expenditure is how many calories you burn per day. You can calculate this manually or use our free macro calculator.

The formula (Mifflin-St Jeor equation):

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 5

Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Then multiply by your activity factor:

• Sedentary (desk job): BMR × 1.2
• Lightly active (1-3 days/week): BMR × 1.375
• Moderately active (3-5 days/week): BMR × 1.55
• Very active (6-7 days/week): BMR × 1.725

Step 2: Set Your Calorie Target

• Fat loss: TDEE − 300 to 500 calories
• Maintenance: TDEE
• Muscle gain: TDEE + 200 to 300 calories

Don’t cut too aggressively. A 500-calorie deficit is the maximum for most people — beyond that, you’ll lose muscle and feel terrible.

Step 3: Set Your Macros

Here’s a solid starting point:

Protein: 1.6–2.2g per kg of body weight This is the most important macro. Higher protein preserves muscle, keeps you full, and has a higher thermic effect (your body burns more calories digesting it).

Fat: 0.7–1.2g per kg of body weight Essential for hormones, brain function, and nutrient absorption. Don’t go below 0.5g/kg — your hormones will suffer.

Carbs: Fill the remaining calories Carbs = (Total calories − protein calories − fat calories) ÷ 4

Example Calculation

80kg male, moderately active, fat loss goal:

• TDEE: ~2,600 calories
• Target: 2,100 calories (500 deficit)
• Protein: 160g (640 cal) — 2g/kg
• Fat: 70g (630 cal) — 0.88g/kg
• Carbs: 208g (830 cal) — remaining calories

That gives you plenty of room for variety. 208g of carbs is roughly: porridge for breakfast, a sandwich for lunch, rice with dinner, and a banana.

The 80/20 Rule

Here’s where IIFYM gets practical. While you can eat anything, most successful IIFYM followers apply the 80/20 rule:

• 80% of your food comes from whole, nutrient-dense sources (lean meats, vegetables, fruits, whole grains, legumes)
• 20% of your food comes from whatever you enjoy (chocolate, pizza, ice cream, crisps)

This ensures you get enough micronutrients, fibre, and overall nutrition while still enjoying the foods that make life worth living.

The 80/20 split isn’t a hard rule — it’s a guideline. Some days it’s 90/10, some days it’s 70/30. The macro totals at the end of the day are what matter.

Common IIFYM Mistakes

1. Ignoring Fibre

You can technically hit your macros eating nothing but protein shakes and gummy bears. Don’t. Aim for 25-30g of fibre daily.

2. Obsessing Over Exact Numbers

If your protein target is 160g and you hit 155g, that’s fine. IIFYM is about hitting the ballpark, not the decimal point.

3. Not Tracking Accurately

IIFYM only works if you know what you’re eating. This is where a good tracking app matters — and where AI-powered photo scanning makes life dramatically easier.

4. Neglecting Micronutrients

Macros matter most for body composition, but you still need vitamins and minerals. Eat your vegetables.

5. Cutting Carbs Too Low

Low carb is not inherently better. Carbs fuel your workouts, support recovery, and keep your brain sharp. Unless you have a medical reason, there’s no need to restrict them.

How to Track IIFYM Effectively

The traditional method: weigh everything on a food scale, look up each ingredient in a database, log it manually.

The modern method: snap a photo of your meal and let AI do the work.

Apps like Chowdown use AI to identify foods from photos and estimate macros instantly. Instead of spending 5 minutes logging each meal, you spend 5 seconds taking a photo. Over a day, that’s 20+ minutes saved.

For IIFYM specifically, you need an app that shows:

• ✅ Individual macro breakdowns (not just calories)
• ✅ Running daily totals
• ✅ Per-meal breakdowns

Chowdown does all three, for free. No subscription needed.

Sample IIFYM Day

To make this concrete, here’s what a 2,100-calorie IIFYM day might look like:

Breakfast — Protein Porridge (450 cal)

• 60g oats, 200ml milk, 30g whey protein, banana
• P: 38g | C: 62g | F: 8g

Lunch — Chicken Wrap (550 cal)

• Tortilla, 150g chicken, avocado, salad, hot sauce
• P: 42g | C: 40g | F: 20g

Snack — Greek Yoghurt & Chocolate (350 cal)

• 200g Greek yoghurt, 30g dark chocolate, honey
• P: 22g | C: 35g | F: 14g

Dinner — Pasta Bolognese (600 cal)

• 80g pasta, 150g lean mince, passata, vegetables, parmesan
• P: 45g | C: 60g | F: 18g

Evening Snack — Protein Ice Cream (150 cal)

• P: 13g | C: 11g | F: 5g

Daily Total: 2,100 cal | P: 160g | C: 208g | F: 65g ✅

Notice: there’s chocolate, pasta, and ice cream in there. That’s IIFYM.

Is IIFYM Right for You?

IIFYM works best for people who:

• ✅ Want flexibility in their food choices
• ✅ Are willing to track what they eat (at least initially)
• ✅ Have basic nutrition knowledge or are willing to learn
• ✅ Don’t have a history of disordered eating (if you do, consult a professional first)

It’s less ideal for:

• ❌ People who prefer strict meal plans with no decisions
• ❌ Those with specific medical dietary requirements
• ❌ Anyone who finds tracking triggering

Getting Started Today

1. Calculate your macros using our free calculator
2. Download a tracker — Chowdown makes it effortless with AI photo scanning
3. Track everything for a week — don’t change your diet, just observe
4. Start adjusting — swap foods to hit your targets while eating what you enjoy

IIFYM isn’t magic. It’s just smart, flexible nutrition. And with modern AI tools removing the friction of tracking, there’s never been a better time to start.

---

Want to start tracking your macros the easy way? Chowdown is a free AI-powered macro tracker — snap a photo and get instant nutrition data.