Intermittent fasting: kick-starting metabolic flexibility

By The Low Carb Clinic, 28 June 2019 - 561 words (3 minutes)

‘Intermittent fasting’ (IF) is when you don’t eat for 14-16 hours, or more. Because IF is such a simple way of addressing obesity and disease, as well as promoting optimal wellbeing, many people choose to do fasts that last 24 hours or more – and it’s easier than it sounds! 

Intermittent fasting: kick-starting metabolic flexibility 

When we eat, our bodies secrete the hormone insulin. Insulin has a very important job – it helps the body to store incoming energy from food. First, it fills up the liver and muscle tissue with glycogen. When these are full, energy is stored as fat. This is why insulin is considered the hormone of fat storage. 

As hunter-gatherers, we were frequently at risk of having to go without food. 

We ate intermittently, depending on availability[1] - so our bodies evolved a mechanism to ensure survival, even in times of famine. Insulin does this to make sure that in lean times, we can sustain ourselves on our energy stockpiles. 

But in our society, we don’t often face famine. We eat regularly – in fact, convenience foods allow us to eat almost continuously. Even to lose weight, we are encouraged to eat 6 small meals a day – and to reduce overall calorie intake[2]. 

But this kind of diet doesn’t help us lose weight. Why? 

When we eat frequently, the constantly high insulin levels mean we can’t access our stored energy. Remember that insulin is the hormone of fat storage. 

To compensate for fewer calories our body reduces its basal metabolic rate (BMR). 

The BMR is the amount of energy your body cells burn, moment to moment. It accounts for 60-75% of your total daily energy expenditure – so it has a huge impact on weight loss[3]. Anyone who has been on a calorie-counting diet has felt the effects of a reduced BMR: you get cold, tired and hungry. 

Intermittent fasting is different. By fasting, we rapidly reduce insulin levels. Low insulin means we can now access the abundance of energy stored in our fat tissue. Just one kilogram of fat stores more than 7000 calories! Unlocking fat means the body simply switches fuel sources: to ketones. This is why prolonged fasting makes you energized, not lethargic. With access to our fat tissue, our bodies don’t have to reduce our BMR. 

The benefits of intermittent fasting don’t stop at weight loss. 

IF also preserves lean muscle: weight loss during IF is more likely to be from fat than from muscle[4] [5]. IF has been shown to positively influence cholesterol and triglyceride levels[6][7], as well as markers of oxidative stress and inflammation[8]. IF appears to encourage cells inside the body to ‘clean up’ common waste products, positively influence free radical metabolism and cellular stress responses, and even mediate age-related changes[9] [10]. 

Because of these metabolic responses, IF is being studied as a treatment for many diseases – from Alzheimer’s and Parkinson’s disease[11], cardiovascular disease[12], to asthma[13] and rheumatoid arthritis[14]. 

IF might also be used to prevent the reoccurrence of certain cancers[15] [16]. Most cancers require glucose as their fuel source, but glucose can be significantly depleted using a combination of a low-carbohydrate diet and IF. While the cells of the body can use ketones as fuel, research is finding that cancer cells can not[17]. 

Won’t I be hungry? 

It might sound hard to fast, but it’s not. And IF has been shown to not result in ‘rebound’ hunger[18]. Even after 36 hours of fasting, levels of ghrelin – the hunger hormone – don’t increase[19]. You’ve got all the energy you need for fasting stored away in your fat tissue – time to unlock it.   

At the Low Carb Clinic, we can help you use IF as another tool to promote weight loss, reverse chronic disease, and optimise wellbeing. Especially if you have a health condition or take medication, we are here to guide and monitor you, to help you achieve your health goals.  

  

 
References

1. Halberg, N., Henriksen, M., Soderhamn, N., & Dela, F. (2005). Effect of intermittent fasting and refeeding on insulin action in healthy men. Journal of Applied Physiology, 99, 2128-2126. doi:doi:10.1152/japplphysiol.00683.2005. 
2. Australian Government National Health and Medical Research Council. (2017). Sample meal plan - men. Retrieved from Eat for Health: https://www.eatforhealth.gov.au/sites/default/files/content/adg_sample_meal_plan_men.pdf 
3. Harvie, M., & Howell, A. (2017). Potential benefits and harms of intermittent energy restriction and intermittent fasting amongst obese, overweight and normal weight subjects - a narrative review of human and animal evidence. MDPI - Behavioural Sciences, 7(4). doi:10.3390/bs7010004 
4. Alhamdan, B., Garcia-Alvarez, A., Alzahrnai, A., Karanxha, J., Stretchberry, D., Contrera, A., & Cheskin, L. (2016). Alternate-day versus daily energy restriction diets: which is more effective for weight loss? A systematic review and meta-analysis. Obesity science & practice, 2(3), 293-302. doi:doi: 10.1002/osp4.52 
5. Gotthardt, J., Verpeut, J., Yeomans, B., Yang, J., Yasrebi, A., Roepke, T., & Bello, N. (2015). Intermittent fasting promotes fat loss with lean mass retention, increased hypothalamic norepinephrine content, increased neuropeptide Y gene expression in diet-induced obese male mice. Endocrinology, 157(2), 679-691. doi: 10.1210/en.2015-1622 
6. Bhutani, S., Klempel, M., Berger, R., & Varady, K. (2010). Improvements in coronary heart disease risk indicators by alternate day fasting involve adipose tissue modulations. Obesity, 18(11), 2152-2159. doi:doi:10.1038/oby.2010.54 
7. Klempel, M., Kroeger, C., Bhutani, S., Trepanowski, J., & Varady, K. (2012). Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women. Nutrition Journal, 11(98). Retrieved from http://www.nutritionj.com/content/11/1/98 
8. Johnson, J., Warren, S., Cutler, R., Martin, B., Dong-Hoon, H., Dixit, V., . . . Nassar, M. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology & Medicine, 42(5), 665-674. doi:10.1016/j.freeradbiomed.2006.12.00 
9. Mattson, M., Longo, V., & Harvie, M. (2016). Impact of intermittent fasting on health and disease processes. Ageing Research Reviews. doi: http://dx.doi.org/10.1016/j.arr.2016.10.005 
10. Anton, S., Moehl, K., Donahoo, W., Marosi, K., Lee, S., Mainous, A., . . . Mattson, M. (2018). Flipping the metabolic switch: understanding and applying health benefits of fasting. Obesity, 26(2), 254-268. doi:10.1002/oby.22065 
11. Shin, B., Kang, S., Kim, D., & Park, S. (2018). Intermittent fasting protects against the deterioration of cognitive function, energy metabolism and dyslipidemia in Alzheimer's disease-induced estrogen deficient rats. Experimental biology and medicine, 243(4), 334-343. doi:10.1177/1535370217751610 
12. Bhutani, S., Klempel, M., Berger, R., & Varady, K. (2010). Improvements in coronary heart disease risk indicators by alternate day fasting involve adipose tissue modulations. Obesity, 18(11), 2152-2159. doi:doi:10.1038/oby.2010.54 
13. Johnson, J., Warren, S., Cutler, R., Martin, B., Dong-Hoon, H., Dixit, V., . . . Nassar, M. (2007). Alternate day calorie restriction improves clinical findings and reduces markers of oxidative stress and inflammation in overweight adults with moderate asthma. Free Radical Biology & Medicine, 42(5), 665-674. doi:10.1016/j.freeradbiomed.2006.12.00 
14. Fraser, D., Thoen, J., Djoseland, O., Forre, O., & Kjeldsen-Kragh, J. (2000). Serum levels of interleukin-6 and dehydroepiandrosterone sulphate in response to either fasting or a ketogenic diet in rheumatoid arthritis patients. Clinical and Experimental Rheumatology, 18(3), 357-362. 
15. Allen, B et al. 2014. ‘Ketogenic diets as an adjuvant cancer therapy: History and potential mechanism.’ Redox Biology, vol. 2, pp. 963-970.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4215472/ 
16. Bozzetti F, Zupec-Kania B. Klempel, M., Bhutani, S., Fitzgibbon, M., Freels, S., & Varady, K. (2010). Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutrition Journal, 9(35). Retrieved from http://www.nutritionj.com/content/9/1/35 2015. ‘Towards a cancer-specific diet,’ Clinical Nutrition, vol.35, pp. 1188-1195 
17. Fine, E., Champ, C., Feinman, R., Marquez, S., & Klement, R. (2016). An evolutionary and mechanistic perspective on dietary carbohydrate restriction in cancer prevention. Journal of evolution and health, 1(1). doi:https://doi.org/10.15310/2334-3591.1036 
18. Varady, K., Bhutani, S., Klempel, M., Kroeger, C., Trepanowski, J., Haus, J., . . . Calvo, Y. (2013). Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutrition Journal, 12(146). Retrieved from http://www.nutritionj.com/content/12/1/146 
19. Heilbronn, L., Smith, S., Martin, C., Anton, S., & Ravussin, E. (2005). Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. The American Journal of Clinical Nutrition, 81, 69-73.