Fasting Tracker

Fasting plans

16:8 vs 18:6: which fasting plan is better?

Two hours apart: how 16:8 and 18:6 compare, what the research shows and how to choose

16:8 and 18:6 side by side

16:8 and 18:6 compared. Both are free in Fasting Tracker.
16:818:6
Fast16 h18 h
Eating window8 h6 h
Name in the appLeangainsFat Burner
LevelIntermediateIntermediate
MealsTwo or threeUsually two
Sample window12:00 p.m. to 8:00 p.m.12:00 p.m. to 6:00 p.m.
Stage when the fast endsFat Burning, just begunFat Burning, two hours in
Protein for 110 g a dayAbout 37 g a meal over three mealsAbout 55 g a meal over two meals

What the extra two hours do

Both plans reach Fat Burning, the stage that begins around 16 hours, when glycogen is low and stored fat has become a major fuel 3. A 16:8 fast ends just as it starts; an 18:6 fast spends two more hours in it. Neither reaches Ketosis, which Fasting Tracker marks at around 24 hours.

  1. 0 hBlood Sugar RisingYour body is digesting your last meal and using that energy. Insulin is elevated.
  2. 4 hBlood Sugar FallingBlood sugar settles back to normal and insulin starts to drop.
  3. 12 hFuel SwitchYour liver's glycogen is getting low, so your body starts turning to fat for fuel.
  4. 16 hFat BurningYour body starts burning stored fat for energy. Stay hydrated!
MYTH
18:6 burns far more fat than 16:8.
FACT
Fat burning ramps up gradually as insulin falls, so two extra hours add a little more of the same stage 3. In a trial that compared a 4-hour window with a 6-hour one, the shorter window didn't do clearly better 1. Over weeks, how much you eat matters more than the last two hours of the fast.

What the research shows

Key study

16:8 alone didn't beat three meals a day

  • Randomized trial
  • 116 adults
  • 12 weeks

People who ate between noon and 8 p.m., without any other advice, lost no more weight than people eating three meals a day, and they lost more lean mass from their arms and legs.

Lowe et al., JAMA Intern Med 2020

Key study

A 6-hour window cut calories without counting

  • Randomized trial
  • 58 adults with obesity
  • 8 weeks

People who ate only within 6 hours, from 1 to 7 p.m., or within 4 hours lost about 3% of their weight compared with a control group, because they ate around 550 fewer calories a day.

Cienfuegos et al., Cell Metab 2020

Two more studies help. In resistance-trained men, 16:8 with the same calories and protein as a normal diet kept muscle and strength and reduced fat mass over 8 weeks 4. And in 8 men with prediabetes, the same food eaten within an early 6-hour window, finishing before 3 p.m., improved insulin sensitivity and blood pressure even without weight loss 5. That was a small study, but it suggests that when you eat may matter as much as how long you fast.

Who each plan suits

16:8 may suit you better if:

  • You're moving up from 13:11 or 14:10 and want a plan you can keep every day.
  • You like three meals, or train hard and need plenty of protein.
  • Your evenings are social and a 6-hour window would often clash with dinner.

18:6 may suit you better if:

  • 16:8 has felt easy for a few weeks and you'd like a step further.
  • Two meals a day already feel natural to you.
  • You can eat early, finishing in the afternoon or early evening 5.

Eating enough protein in 6 hours

The main cost of a shorter window is protein. Gains from strength training level off at about 1.6 g of protein per kilo of body weight a day 6: about 110 g for a 70 kg person. On 18:6 that usually means two meals of around 55 g each. That's fine: your body keeps using a large serving for many hours 7. If your window allows three meals, spreading protein across them is a little better still 8. The protein calculator works out your own target.

Trying 18:6

  1. Spend at least two comfortable weeks on 16:8 first.
  2. Try 18:6 on a few days a week before making it daily.
  3. Move dinner earlier rather than breakfast later, if your days allow it.
  4. Build both meals around protein, vegetables and fibre 9.
  5. Go back to 16:8 on busy or social days. Both plans are free in Fasting Tracker, so switching costs nothing.

Sources

  1. Cienfuegos S, Gabel K, Kalam F, et al. Effects of 4- and 6-h Time-Restricted Feeding on Weight and Cardiometabolic Health: A Randomized Controlled Trial in Adults with Obesity. Cell Metab. 2020;32(3):366-378.e3. doi.org/10.1016/j.cmet.2020.06.018
  2. Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Intern Med. 2020;180(11):1491-1499. doi.org/10.1001/jamainternmed.2020.4153
  3. Anton SD, Moehl K, Donahoo WT, et al. Flipping the Metabolic Switch: Understanding and Applying the Health Benefits of Fasting. Obesity (Silver Spring). 2018;26(2):254-268. doi.org/10.1002/oby.22065
  4. Moro T, Tinsley G, Bianco A, et al. Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med. 2016;14(1):290. doi.org/10.1186/s12967-016-1044-0
  5. Sutton EF, Beyl R, Early KS, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab. 2018;27(6):1212-1221.e3. doi.org/10.1016/j.cmet.2018.04.010
  6. Morton RW, Murphy KT, McKellar SR, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018;52(6):376-384. doi.org/10.1136/bjsports-2017-097608
  7. Trommelen J, van Lieshout GAA, Nyakayiru J, et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Rep Med. 2023;4(12):101324. doi.org/10.1016/j.xcrm.2023.101324
  8. Areta JL, Burke LM, Ross ML, et al. Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 2013;591(9):2319-31. doi.org/10.1113/jphysiol.2012.244897
  9. Leidy HJ, Clifton PM, Astrup A, et al. The role of protein in weight loss and maintenance. Am J Clin Nutr. 2015;101(6):1320S-1329S. doi.org/10.3945/ajcn.114.084038
  10. Grajower MM, Horne BD. Clinical Management of Intermittent Fasting in Patients with Diabetes Mellitus. Nutrients. 2019;11(4):873. doi.org/10.3390/nu11040873

A note on health

Fasting Tracker is designed for general wellness and is not a medical device. Fasting is not right for everyone. If you are pregnant, diabetic, have a history of eating disorders or take medication, talk to your doctor first, and before any extended fast.