12-Hour Fasting – A Key Strategy For A Longer, Healthier Life

You’d be hard pressed to find someone who didn’t know that if you want to be healthy, you should eat primarily healthy food.

But what you might not know is, the timing of what you eat matters just as much as what you eat; and there is growing evidence that 12-hour fasting is so protective of health that it can even attenuate the effects of a high-fat diet.

What Is 12-Hour Fasting?

Also called time-restricted feeding (TRF), 12-hour fasting confines food consumption to a 12-hour window or – put another way – is the practice of, during a 24-hour period, maintaining a 12-hour window where no food is consumed.

In practice this may mean that any and all meals/snacks are consumed between 7am and 7pm, with no food being consumed between 7pm and 7am (or 8am-8pm as another example).

Some studies actually define time-restricted feeding as an 8-9 hour period, which also shows benefit although not as realistic or easy to achieve as 12 hours.

But Why?

There has been a lot of research done on many different types and variations of fasting, but I like this particular type of fasting for both what the evidence says, and the logic behind it.

There was a time when, in all likelihood, humankind rose with the sun – and days effectively ended with sundown. With no electricity, and only flame for light, food preparation and consumption would have been mostly confined to daylight hours.

Nowadays, with access to electricity, we can make meals in the dark well before dawn, and – especially given the long hours some of us keep – make dinner well after sunset. This has led to a shift in our diurnal biorhythms for many reasons, including the fact that food consumption is also an immunological provocation.

The potential for food to be inflammatory means our bodies produce cortisol in response to eating [1] and, in the evening, this can mess with our sleep cycles as cortisol interferes with melatonin affecting sleep quality. Erratic eating patterns also increase the risk of disease[2], and seem to widely disrupt normal physiological processes[3].

Because eating at an unusual time of day (during the night for us) can desynchronise our biological clock and can cause obesity and metabolic disorders by inducing leptin resistance, overeating, physical inactivity, hepatic (liver) fat accumulation and fat gain[4] as well as obesity, diabetes, and metabolic syndrome[5] – it is not so surprising that data is emerging to suggest that increasing the fasting period between our last meal of the day and the first meal of the following day may beneficially impact body weight and metabolic health.

Research says TRF may prevent and reverse obesity, along with other associated issues:

  • prevents excessive body weight gain, improves sleep, and attenuates age- and diet- induced cardiovascular disease[6]
  • even in a high-fat diet (HFD):**
    • when consumption was limited to an 8-hour window TRF without caloric restriction was an effective strategy for alleviating the negative effects of a HFD on body weight, liver weight, and glucose tolerance[7]
    • improvement in insulin resistance and a reduced severity of hepatic steatosis was seen using TRF[8]
    • TRF also reduced high-fat, diet-induced increases in adiposity and pro-inflammatory cytokines[9]
  • efficacy for weight loss and improvements in multiple health indicators including insulin resistance[10]
  • stabilised and reversed the progression of metabolic diseases in mice with preexisting obesity and type II diabetes[11]
  • improved sleep, prevention of body weight gain, and deceleration of cardiac ageing[12]
  • correlated with protection from breast cancer[2]
  • had an anticonvulsant effect[13]
  • may effect the gut microbiome[14]

** this is not a license to eat badly during the 12-hour ‘active/eating window’ but rather a demonstration of the profound effect of time-restricted feeding.

How To Do 12-Hour Fasting

As mentioned above this will look, for most people, like meals/snacks are consumed between 7am and 7pm, with no food being consumed between 7pm and 7am. Or, the same could be done using 8am-8pm-8am.

Where this can become tricky is if you have a long commute to and from work, or a different work schedule to your partner, or work particularly long days/shift work/on the road. Shift workers are particularly at risk as it appears issues with blood sugar and insulin balance might be affected with eating during dark hours[15] and they may end up eating more, and moving less[16].

The good news is that even doing 12-hour fasting for just 5 days a week still makes a large difference[17].


When it comes to strategies of how you might be able to balance eating with fasting for 12 hours – a little preparation can go a long way!

  • Practice 12-hour fasting Sunday-Thursday knowing that, even if you have late dinners on a Friday and Saturday night, it will still be useful
  • Breakfast is probably the easiest place to adjust your routine as there are a number of good breakfasts that can be made the night before (or several nights before) and function as grab-and-go:
    • Overnight oats can be prepared the weekend before and made into delicious single serve jars that can be eaten on the way to, or once you’ve arrived at, work. You can download my recipe here.
    • Mini egg frittatas are also good for on-the-run – loaded with veggies and protein they’re a great way to start the day. Here’s some recipe inspiration.
  • Additionally – when it comes to dinner, any preparation you can do prior to cooking/mealtime will bring the time that you eat forward quite significantly:
    • If you have time in the morning, you can prep the veggies by peeling and cutting – you may even be able to do this on the weekend if necessary. This way, when you get home from work, you can immediately start the cooking process.
    • Slow-cooker recipes are also helpful as you can set and forget in the morning, and dinner is ready when you get home
    • Making extra at mealtimes in order to have food leftovers can also work – reheating time is much less than prep and cooking time!

Tell me, have you tried 12-hour fasting yourself? If you have any tips or comments you’d like to share, I’d love to hear them in the comments below!




    1. Stimson RH, Mohd-Shukri NA, Bolton JL, Aet al. The postprandial rise in plasma cortisol in men is mediated by macronutrient-specific stimulation of adrenal and extra-adrenal cortisol production.J Clin Endocrinol Metab. 2014;99(1):160-8.
    2. Manoogian EN, Panda S. Circadian rhythms, time-restricted feeding, and healthy aging. Ageing Res Rev. 2016. pii: S1568-1637(16)30301-4.
    3. Opperhuizen AL, Wang D, Foppen E, et al. Feeding during the resting phase causes profound changes in physiology and desynchronization between liver and muscle rhythms of rats. Eur J Neurosci. 2016;44(10):2795-2806.
    4. Yasumoto Y, Hashimoto C, Nakao R, et al. Short-term feeding at the wrong time is sufficient to desynchronize peripheral clocks and induce obesity with hyperphagia, physical inactivity and metabolic disorders in mice. Metabolism. 2016;65(5):714-27.
    5. Mukherji A, Kobiita A, Damara M, et al. Shifting eating to the circadian rest phase misaligns the peripheral clocks with the master SCN clock and leads to a metabolic syndrome. Proc Natl Acad Sci U S A. 2015;112(48):E6691-8.
    6. Melkani GC, Panda S. Time restricted feeding for prevention and treatment of cardiometabolic disorders. J Physiol. 2017 Mar 10. doi: 10.1113/JP273094. [Epub ahead of print]
    7. Duncan MJ, Smith JT, Narbaiza J, et al. Restricting feeding to the active phase in middle-aged mice attenuates adverse metabolic effects of a high-fat diet. Physiol Behav. 2016;167:1-9. 
    8. Chung H, Chou W, Sears DD, et al. Time-restricted feeding improves insulin resistance and hepatic steatosis in a mouse model of postmenopausal obesity. Metabolism. 2016;65(12):1743-1754.
    9. Sundaram S, Yan L. Time-restricted feeding reduces adiposity in mice fed a high-fat diet. Nutr Res. 2016;36(6):603-11.
    10. Mattson MP, Longo VD, Harvie M. Impact of intermittent fasting on health and disease processes. Ageing Res Rev. 2016 Oct 31. pii: S1568-1637(16)30251-3. 
    11. Chaix A, Zarrinpar A, Miu P, et al. Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Cell Metab. 2014;20(6):991-1005.
    12. Gill S, Le HD, Melkani GC, et al. Time-restricted feeding attenuates age-related cardiac decline in Drosophila. Science. 2015 Mar 13;347(6227):1265-9.
    13. Landgrave-Gómez J, Mercado-Gómez OF, Vázquez-García M, et al. Anticonvulsant Effect of Time-Restricted Feeding in a Pilocarpine-Induced Seizure Model: Metabolic and Epigenetic Implications. Front Cell Neurosci. 2016;10:7.
    14. Zarrinpar A, Chaix A, Yooseph S, et al. Diet and feeding pattern affect the diurnal dynamics of the gut micro biome. Cell Metab. 2014;20(6):1006-17.
    15. Mukherji A, Kobiita A, Chambon P. Shifting the feeding of mice to the rest phase creates metabolic alterations, which, on their own, shift the peripheral circadian clocks by 12 hours. Proc Natl Acad Sci U S A. 2015 Dec 1;112(48):E6683-90. 
    16. Yasumoto Y, Hashimoto C, Nakao R, et al. Short-term feeding at the wrong time is sufficient to desynchronize peripheral clocks and induce obesity with hyperphagia, physical inactivity and metabolic disorders in mice. Metabolism. 2016;65(5):714-27.
    17. Olsen MK, Choi MH, Kulseng B, et al. Time-restricted feeding on weekdays restricts weight gain: A study using rat models of high-fat diet-induced obesity. Physiol Behav. 2017 May 1;173:298-304. 


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