16:8 vs OMAD vs 5:2: Which Intermittent Fasting Protocol Should You Choose?

Decided to try intermittent fasting but lost among so many protocols? 16:8, 18:6, 20:4, OMAD, 5:2…

Each one has its advantages and disadvantages. Let’s compare so you can choose consciously.

The Main Protocols

16:8 (Leangains)

Structure:
- 16 hours of fasting
- 8 hours of eating window
- Example: Eat from 12pm to 8pm

Popularized by: Martin Berkhan

18:6

Structure:
- 18 hours of fasting
- 6 hours of eating window
- Example: Eat from 2pm to 8pm

More restrictive version of 16:8

20:4 (Warrior Diet)

Structure:
- 20 hours of fasting (or very light eating)
- 4 hours of eating window
- Usually one large meal at night

Popularized by: Ori Hofmekler

OMAD (One Meal A Day)

Structure:
- ~23 hours of fasting
- 1 meal per day
- All eating in ~1 hour

The most extreme of the daily protocols

5:2

Structure:
- 5 days eating normally
- 2 non-consecutive days of ~500-600 calories

Different: It's not daily fasting, it's weekly

Eat-Stop-Eat

Structure:
- 1-2 24h fasts per week
- Remaining days: Normal eating

Popularized by: Brad Pilon

Detailed Comparison

Ease of Adherence

Easier → Harder:

16:8 ████████░░ (8/10)
- Just skip breakfast
- 2-3 normal meals
- Socially easier

18:6 ██████░░░░ (6/10)
- Smaller window
- 2 large meals
- Requires more planning

5:2  ██████░░░░ (6/10)
- 5 free days is good
- But 2 days of severe restriction
- Requires punctual discipline

20:4 ████░░░░░░ (4/10)
- Very short window
- Hard to eat enough
- Digestive discomfort common

OMAD ███░░░░░░░ (3/10)
- Extreme
- Nutritionally difficult
- Not sustainable for most

Suitability For Training

Better → Worse for those who train:

16:8 ████████░░ (8/10)
- Time for pre and post-workout
- 2-3 protein meals
- Timing flexibility

18:6 ██████░░░░ (6/10)
- Still ok
- Need to plan workout within window
- 2 protein meals

5:2  ██████░░░░ (6/10)
- 5 normal days to train
- Restriction days: Rest or light
- Periodize with training

20:4 ████░░░░░░ (4/10)
- Hard to fit training
- Little distributed protein
- Compromised recovery

OMAD ██░░░░░░░░ (2/10)
- Terrible for hypertrophy
- One protein dose per day
- Not recommended for serious training

Fat Loss

All work IF they create a caloric deficit.

16:8 ████████░░
- Good natural deficit
- Sustainable long term

18:6 ████████░░
- Slightly larger deficit
- Still sustainable

20:4 ████████░░
- Significant deficit
- Hard to overeat

OMAD █████████░
- Almost impossible to eat in surplus
- Guaranteed deficit

5:2  ████████░░
- ~3000 cal guaranteed weekly deficit
- "Freedom" days help psychologically

Note: More extreme ≠ more effective. Long-term adherence matters more.

Muscle Preservation

Better → Worse for keeping muscle:

16:8 ████████░░ (8/10)
- Multiple protein doses
- Fed training possible
- Studies show ok preservation

5:2  ███████░░░ (7/10)
- 5 normal days preserve well
- On low days, prioritize protein
- Train on normal days

18:6 ██████░░░░ (6/10)
- Less window for protein
- Still possible to preserve
- Requires attention

20:4 ████░░░░░░ (4/10)
- Hard to distribute protein
- Compromised protein synthesis
- Risk of muscle loss

OMAD ███░░░░░░░ (3/10)
- One protein dose = suboptimal
- High risk of muscle loss
- Not recommended for preservation

Analysis By Protocol

16:8 - The Gold Standard

How it works in practice:

Example day:
07:00 - Wake up (water, black coffee)
12:00 - First meal (lunch)
3:30pm - Second meal (snack)
7:30pm - Third meal (dinner)
8:00pm - Window closes

Pros:

✅ Most researched
✅ Easy to follow (skip breakfast)
✅ Socially acceptable
✅ Allows 3+ meals
✅ Flexible for training
✅ Sustainable long term

Cons:

❌ May not be restrictive enough for some
❌ Easy to "exceed" the window
❌ Still requires caloric control

For whom:

✅ IF beginners
✅ Those who train
✅ Those who want something sustainable
✅ Most people

18:6 - The Middle Ground

How it works in practice:

Example day:
07:00 - Wake up
2:00pm - First meal
5:00pm - Second meal
7:30pm - Third meal (if it fits)
8:00pm - Window closes

Pros:

✅ More restrictive than 16:8
✅ Still allows 2-3 meals
✅ Good for those adapted to 16:8

Cons:

❌ Larger meals
❌ Less flexibility
❌ Can be difficult socially

For whom:

✅ Those already doing 16:8 who want more restriction
✅ Those who naturally don't feel hungry until late
✅ More aggressive cutting

20:4 - Warrior Diet

How it works in practice:

Example day:
During the day: Water, coffee, raw vegetables (minimum)
6:00pm-10:00pm: Eating window
One large meal + possible snack

Pros:

✅ Extreme simplicity
✅ Almost guaranteed deficit
✅ Some report mental clarity
✅ Can work for some profiles

Cons:

❌ Very restrictive
❌ Hard to eat enough nutrients
❌ Digestive discomfort (huge meals)
❌ Bad for those who train
❌ Risk of binge

For whom:

⚠️ Specific people who adapt
⚠️ Short-term aggressive cutting
❌ Not for most
❌ Not for serious training

OMAD - One Meal A Day

How it works in practice:

Example day:
All day: Water, coffee, tea
7:00pm-8:00pm: One large meal
All caloric intake in ~1h

Pros:

✅ Maximum simplicity
✅ Guaranteed deficit
✅ Zero decisions about food until the meal
✅ Can work for some in extreme cutting

Cons:

❌ Extremely difficult nutritionally
❌ Almost impossible to reach adequate protein
❌ Severe digestive discomfort
❌ Not sustainable for most
❌ Terrible for hypertrophy
❌ Risk of disordered eating behavior
❌ Nutritional deficiencies likely

For whom:

⚠️ Very specific situations
⚠️ People who tried everything and only this works
❌ Not recommended in general
❌ Definitely not for those who train

5:2 - Weekly Intermittent Fasting

How it works in practice:

Example week:
Monday: Normal (~2000 cal)
Tuesday: Restricted (~500-600 cal)
Wednesday: Normal
Thursday: Normal
Friday: Restricted (~500-600 cal)
Saturday: Normal
Sunday: Normal

Pros:

✅ 5 days of "freedom"
✅ Easier socially
✅ Flexibility on normal days
✅ Guaranteed weekly deficit (~3000 cal)
✅ Can adjust restriction days

Cons:

❌ 2 days of intense hunger
❌ Can be hard to train on restricted days
❌ Risk of overcompensating on free days
❌ Less researched than daily fasting

For whom:

✅ Those who don't want daily restriction
✅ Those who travel a lot / intense social life
✅ Those who can be disciplined for 2 days
✅ Cutting with more flexibility

How to Choose Your Protocol

Decision Flowchart

Do you train hard and want to gain muscle?
├── Yes → DON'T do IF or use 16:8 at most
└── No → Continue ↓

Are you cutting?
├── Yes → 16:8, 18:6, or 5:2
└── No → You probably don't need IF

Do you naturally skip breakfast?
├── Yes → 16:8 will be easy
└── No → Consider 5:2 or don't do IF

Do you want something simple day-to-day?
├── Yes → 16:8
└── No → 5:2 might give more freedom

Have you already done 16:8 and want more?
├── Yes → Test 18:6
└── No → Stay with 16:8

By Goal

Fat loss (beginner):
→ 16:8 (most sustainable)

Fat loss (aggressive):
→ 18:6 or 5:2

Maintenance:
→ 16:8 if you like it, otherwise you don't need it

Hypertrophy:
→ Don't do IF (or 16:8 at most, adapted)

Maximum simplicity:
→ 16:8 or OMAD (but OMAD has many cons)

By Lifestyle

Work in the morning, train in the afternoon:
→ 16:8 (skip breakfast, eat post-workout)

Work at night:
→ Adapt window to your schedule

Intense social life:
→ 5:2 (more free days)

Travel a lot:
→ 5:2 or flexible 16:8

Athlete / train 2x per day:
→ Don't do IF

Common Mistakes

Mistake 1: Choosing the Most Extreme

❌ "If 16:8 is good, OMAD is better"
→ More extreme ≠ more effective
→ Long-term adherence matters
→ Start light, adjust later

Mistake 2: Ignoring Calories

❌ "I'm fasting, I can eat whatever I want"
→ IF is not a free pass
→ You still need a deficit to lose weight
→ Food quality still matters

Mistake 3: Being Too Rigid

❌ "I ate 5 min before the window opened, I failed"
→ IF is a tool, not a religion
→ Flexibility helps adherence
→ 1h more or less doesn't change anything

Mistake 4: Ignoring Training

❌ "I'm going to train hard after 20h fasted"
→ Performance will drop
→ Recovery compromised
→ Adapt protocol to training, not the opposite

Mistake 5: Forcing When It Doesn’t Work

❌ "Everyone does IF, I have to do it"
→ IF is not mandatory
→ Some people don't adapt
→ If you're suffering: Stop

Transitioning Between Protocols

From Nothing to 16:8

Week 1: Delay breakfast 1-2h
Week 2: Delay breakfast 3-4h
Week 3: Skip breakfast, first meal at 11am-12pm
Week 4: Establish 16:8 window

From 16:8 to 18:6

Week 1-2: Reduce window by 30min
Week 3-4: Reduce another 30min
Week 5+: Establish 18:6

Going Back

If a protocol isn't working:
→ There's no shame in backing off
→ 16:8 → normal eating is ok
→ 20:4 → 16:8 is sensible
→ Listen to your body

Final Summary:

Protocol	Difficulty	For Training	Sustainability	Recommendation
16:8	Easy	Good	High	✅ For most
18:6	Medium	Ok	Medium	⚠️ After adapting to 16:8
20:4	Hard	Poor	Low	⚠️ Specific cases
OMAD	Very hard	Terrible	Very low	❌ Not recommended
5:2	Medium	Variable	Medium-High	✅ Valid alternative

Start simple. 16:8 is enough for most people. If it works well and you want more restriction, adjust gradually.

Remember: the best protocol is the one you can maintain while achieving your goals. There’s no prize for being more extreme.

References:

Varady KA, et al. “Alternate-day fasting and chronic disease prevention: a review of human and animal trials.” Am J Clin Nutr. 2007.
Harvie MN, et al. “The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers.” Int J Obes. 2011.
Trepanowski JF, et al. “Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection.” JAMA Intern Med. 2017.
de Cabo R, Mattson MP. “Effects of Intermittent Fasting on Health, Aging, and Disease.” N Engl J Med. 2019.