Intermittent Fasting and the 5:2 Diet

Chapter summary

Animals and humans do not eat the same amount every day, yet they hold a normal weight range by adjusting intake. The only mammals that become obese are humans and animals fed by humans, such as pets.
Western habits of three meals plus constant grazing are unusual. Eating five meals a day may be harmful, although this claim meets some medical opposition.
Hugh used MyFitnessPal for six months. A normal woman eats about 2,000 calories and a man about 2,400, and needs about 200 fewer between age 20 and 60. To lose 0.5kg a week he ate about 1,800 falling to 1,600 calories a day, with 600-calorie fasting days.

Michael Mosley’s BBC documentary (2012): A four-day supervised fast halved his IGF-1 (a marker linked to cancer risk), lowered glucose and cut 1.5kg of fat. Valter Longo (USC) said periodic fasting may give long-lasting benefits.
Alternate-day fasting: Krista Varady (University of Illinois) had obese women eat 25% of calories one day and 125% the next, with good results. Mosley found it socially hard and emotionally demanding.
The 5:2 plan: Mosley chose 25% of calories on two days a week. This became The Fast Diet and has sold to hundreds of thousands.
Animal studies: Mice on a high-fat diet fed within a restricted window had better health than mice grazing on the same food. Mark Mattson’s mice on intermittent restriction did not develop detectable dementia, while junk-fed mice became fat and died young.
Exercise and the brain: Aerobic exercise increases hippocampus size and memory (Erickson 2011).

Calorie restriction for long life: CRONies (over 50,000 followers) cut calories permanently, based on mouse studies showing up to 50% longer life. Partridge’s fruit fly work found it was not simply calories, but particular nutrients.
Proven in humans? No. The documentary linked animal and human results, and viewers may think it is a sure-fire solution. The author says it is work in progress.
Medical caution: Some doctors oppose fasting. Online forums report yo-yo dieting and eating-disorder issues for some people, though other factors may be involved. Fasting is not suitable for everyone, so check with your doctor.
Author’s experience: He found it easy and flexible.

Mind: It removes guilt and “bad foods” on normal days.
Portion size: You learn portions and may shift to less sugar and more protein.
Willpower: It is one day at a time.
Social: Choose two quiet days and keep socialising on the others. With 30% or more of food eaten out, a daily diet is a big social barrier.

Mosley, M. and Spencer, M. (2013) The Fast Diet. Short Books.
Mair, W., Piper, M. and Partridge, L. (2005) Calories do not explain extension of life span by dietary restriction in Drosophila. PLoS Biol 3(7):e223.
Spindler, S. (2010) Biological effects of calorie restriction: implications for modification of human aging. The Future of Aging.
Erickson, K. et al. (2011) Exercise training increases size of hippocampus and improves memory. PNAS.
Shirayama, Y. et al. (2002) Brain-derived neurotrophic factor produces antidepressant effects in behavioral models of depression. J Neurosci 22(8):3251-3261.