Cardio for Fat Loss — What Actually Works
HIIT vs steady state vs Zone 2 for fat loss. What the research says and what actually works when you are trying to get lean without killing your lifts.
The Dirty Secret About Cardio
Cardio does not burn much fat. A hard 45-minute session might burn 400-500 calories. A single Chipotle burrito is 1100. You cannot outrun a bad diet, and people who try usually fail within 90 days.
What cardio does do: improves recovery, increases work capacity, manages stress, and protects your heart. Those are all reasons to train it. Fat loss is a side effect of eating less.
With that out of the way, here is what works.
Zone 2 (Low-Intensity Steady State)
60-70% of max heart rate. Brisk walk or slow jog. You can hold a conversation.
The Peter Attia favorite. Builds cardiovascular capacity without wrecking your legs for lifting. Sustainable for years. Boring.
Dose: 2-3 sessions of 30-60 minutes per week.
HIIT (High-Intensity Intervals)
Short bursts at 90%+ effort with rest intervals. 30 seconds on, 90 off. 4-8 rounds.
HIIT works, but it is not magic. The metabolic afterburn (“EPOC”) people cite is small — maybe 6-15% of the workout’s total calorie burn. HIIT is useful because it is efficient, not because it burns fat hours later.
Dose: 1-2 sessions of 15-25 minutes per week. Not before leg day.
Steady State Cardio
65-80% of max heart rate. Running, cycling, rowing. Harder than Zone 2 but sustainable for 30-60 minutes.
Most gyms sell this as the fat-loss cardio. It works. It also makes you hungrier than Zone 2, which is the hidden cost. If you cannot control your eating after a long run, steady state can backfire.
Dose: Optional. Replace one Zone 2 session per week if you want variety.
The Sustainable Plan
For fat loss specifically:
- 3 Zone 2 sessions per week (30-45 min walks or easy bike)
- 1 HIIT session per week (15 min, optional)
- 8,000-10,000 steps per day outside of training
That is it. The food is the lever. Cardio supports the effort.
What Kills Most People’s Cardio
Doing too much. A 90-minute run on Saturday does not unlock a lean physique — it unlocks injuries and compensatory eating. Consistency beats intensity. Four walks per week forever beats two marathons per year.
If You Hate Cardio
Walk. Seriously. The research on 10,000 steps per day is modest, but the research on people who walk consistently and eat less is excellent. Everything else is optimization.
Frequently Asked Questions
Is HIIT better than steady-state cardio for fat loss?
For pure fat loss, total calorie burn matters more than the method. HIIT is efficient when time is limited. Steady-state is gentler and easier to recover from.
How much cardio should I do to lose fat?
2-4 sessions per week combined with a caloric deficit. Diet does 80% of the work. Cardio is there to accelerate and maintain.
Will cardio kill my gains?
Not if you keep it to 2-3 hours per week total. Excessive cardio (more than 4-5 hours) interferes with muscle recovery and strength gains.
What is Zone 2 cardio?
Zone 2 is 60-70% of your max heart rate. For most people, that is a brisk walk or easy jog where you can still hold a conversation. It builds cardiovascular base without wrecking legs.
Is walking enough cardio?
For most people in a caloric deficit, yes. 8,000-10,000 steps per day plus strength training is a complete fitness program for fat loss.
Should I do cardio in the morning or evening?
Whenever you will actually do it. Fasted morning cardio has no meaningful fat-loss advantage over fed cardio. Pick your schedule.
How long until I see fat loss from cardio?
Visible changes take 4-8 weeks of consistent training and caloric deficit. If the scale has not moved after 6 weeks, adjust calories down.
Can I do cardio every day?
Light cardio (walks, easy cycling) yes. Hard cardio (HIIT, hard intervals) no. Your body needs 1-2 full rest days per week.
What heart rate should I target for fat loss?
For steady-state fat loss, target 65-75% of max heart rate. Calculate max as 220 minus your age. For a 30-year-old that is 124-143 bpm.
Does cardio build muscle?
Generally no. Cardio maintains cardiovascular fitness and supports recovery, but muscle growth requires resistance training and progressive overload.