One of the key strategies we use here at The Natural Nutritionist is a longer overnight fast, which creates a shorter eating window, known in the literature as time restricted feeding (TRF). We originally adopted this strategy for digestive ease and the development of metabolic flexibility and fat adaptation, but there are so many additional day-to-day and long term benefits.
In this article we look closer at the research and help you determine what is the best fasting to eating ratio, and explore when it isn’t the right time to fast.
What are the benefits of time restricted feeding (TRF)?
In the words of one of the leading researchers in this field, Dr Satchin Panda, breakfast starts the daily orchestra of the body and switches on the genes that synchronize the circadian clocks of the body1. These clocks are significantly influenced by food (more so than light) and located in virtually every cell of the body. Dr Panda also states, “it’s a dogma that a high-fat diet leads to obesity and that we should eat frequently when we are awake. Our findings, however, suggest that regular eating times and fasting for a significant number of hours a day might be beneficial to our health”. On the other hand, irregular eating can disrupt your metabolism and as science shows, increases your risk of disease. Controlling the timing of your food therefore, is a powerful way to control your health and disease risk.
The key benefits of TRF are:
- Digestive ease – as digestion is a significantly high energy requiring process, eating less frequently can support digestive health.
- Fat loss – without the presence of circulating glucose, we increase fatty acid oxidation and can burn body fat, rather than store it.
- Development of metabolic flexibility and fat adaptation – TRF is a powerful tool to becoming a fat adapted athlete.
- Improved sleep – melatonin receptors turn off pancreas activity, so it is beneficial to eat 2-3 hours before bed time (before melatonin is at its highest).
- Increased endurance – early research shows an increase in endurance with an 9 hour eating window and therefore 15 hour fast2.
- A potential increased muscle mass development – the science is still in animal models, but restricting feeding times to 12 hours can lead to increased muscle mass regardless of food quality2.
- Breast cancer protection – a 13 hour fast in women has been shown to be protective to breast cancer 3, 4.
- Chronic disease risk reduction, including inflammation cardiovascular disease prevention5, 6.
So what is the ideal eating window?
12:12 (12 hours fasting, 12 hours eating)
A 12:12 is a great place to start as one of the simplest strategies to optimizing your metabolism (whether to become a fat adapted athlete, to assist fat loss or to improve cognitive function) is to delay breakfast. if you have been habitually eating dinner late of an evening and/or eating breakfast as soon as you rise, start planning your eating times to allow for 12 hours between dinner and breakfast the next day. Remember, the definition of breakfast is “breaking the fast”, so while it is still the most important meal of the day, it definitely doesn’t need to be consumed at 7am on the dot. From a practical standpoint, if you regularly eat dinner at 8pm, you will need to make portable breakfast choices to eat at your desk at 8am, but with some forward thinking and simple preparation, this is more than possible. Some of our favourite portable breakfasts include:
13:11 (13 hours fasting, 11 hours eating)
A 13:11 is one of our favourite strategies as it is quite easily implemented as a circadian rhythm fast. Eating in line with your circadian rhythm has many benefits, and short term, notably, improved sleep. As we have discussed, it is ideal to eat at least 2-3 hours before bed, before melatonin levels peak. An example of a circadian fast will depend on what time you go to bed, but two examples are:
- Bed time of 9pm: dinner at 6-7pm and breakfast at 7-8am
- Bed time of 10.30pm: dinner at 7.30-8.30pm and breakfast at 8.30-9.30am
16:8 (16 hours fasting, 8 hours eating)
A 16:8 is by far the most protective from a disease risk point of view. Research shows not only breast cancer protection in women 3, 4, but decreased risk factors for cardiovascular disease in both men and women 5, 6. Logistically it can be more challenging, but prior planning prevents poor performance, as always. A simple example is to eat dinner by 7pm and break your fast at 11am. In women of child-bearing age we recommended the inclusion of fats in this fasting ratio, such as a Bulletproof Coffee. It is still controversial as to whether this will achieve the longer term health benefits of a complete fast, so please keep this in mind, relative to your goals.
Your fasting muscle
Please note that it is important that you should first train your “fasting muscle”. We do not recommend attempting a 16:8 until you have competently completed both 13:11 and 12:12. After you do break your fast, factors such as your ongoing satiety and exercise recovery will dictate whether you have been successful. If you fast for too long for example, you may find that you are needing to graze following your first meal, or you may feel more fatigued in the day or days post-workout. Simply track these parameters as a way to determine when you can safely extend your overnight fast.
From an exercise standpoint, please ensure you eat within the hour after a high intensity session. This will mean you will need to be able to finish your session at or before 15 hours into your fast. Aerobic training, which is (or should be) predominantly fuelled on fat is safer to complete earlier in your fasting window as muscle glycogen replenishment is not a primary goal at this point in time.
When shouldn’t you fast?
Fasting is clearly extremely beneficial for our health, but it isn’t for everyone. Quite simply, it should not be attempted under the following circumstances:
- During pregnancy or breast feeding.
- During periods of high stress and/or adrenal dysfunction.
- If you are takin certain medications, including insulin.
- If you have poor blood sugar control. As always, start with real food first and improve your satiety and metabolism before your dive in the deep end with TRF.
- After high intensity training, as discussed.
Want to learn more? Listen to Episode 123 of The Real Food Reel here.
1 My Circadian Clock: https://mycircadianclock.org
2 Chaix A et al., 2014. Time Restricted Feeding Is a Preventative and Therapeutic Intervention against Diverse Nutritional Challenges. Cell Metabolism, 20, 6, 991-1005.
3 Marinac CR et al., 2015. Prolonged Nightly Fasting and Breast Cancer Risk: Findings from NHANES (2009-2010). Cancer Epidemiology, Biomarkers & Prevention, 24, 783-9.
4 Marinac CR et al., 2016. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncology, 2, 8, 049-1055.
5 St-Onge M et al., 2017. Meal Timing and Frequency: Implications for Cardiovascular Disease Prevention: A Scientific Statement From the American Heart Association. Circulation, 135, 25, 00-00.
6 Shen R et al. 2016. Neuronal energy-sensing pathway promotes energy balance by modulating disease tolerance. Proceeding of the National Academy of Sciences of the United States of America, 113, 23, E3307–E3314.
Image credit here.