The ideas behind the diet are not supported by scientific evidence.
The Zone diet proposes that a relatively narrow distribution in the ratio of proteins to carbohydrates, centered at 0.75, is essential to "balance the insulin to glucagon ratio, which purportedly affects eicosanoid metabolism and ultimately produces a cascade of biological events leading to a reduction in chronic disease risk, enhanced immunity, maximal physical and mental performance, increased longevity and permanent weight loss."
The diet advocates eating five times a day, with 3 meals and 2 snacks, and includes eating proteins, carbohydrates - those with a lower glycemic index are considered more favorable, and fats (monounsaturated fats are considered healthier) in a caloric ratio of 30%-40%-30%. The hand is used as the mnemonic tool; five fingers for five times a day, with no more than five hours between meals. The size and thickness of the palm are used to measure protein while two big fists measure favorable carbohydrates and one fist unfavorable carbohydrates. There is a more complex scheme of "Zone blocks" and "mini-blocks" that followers of the diet can use to determine the ratios of macronutrients consumed. Daily exercise is encouraged.
As of 2013, there were "no cross-sectional or longitudinal studies examining the potential health merit of adopting a Zone Diet per se, [and] closely related peer-reviewed findings from scientific research cast strong doubt over the purported benefits of this diet. When properly evaluated, the ideas and arguments of popular low carbohydrate diet books like the Zone rely on poorly controlled, non-peer-reviewed studies, anecdotes and non-science rhetoric."
- Cheuvront SN The Zone Diet phenomenon: a closer look at the science behind the claims. J Am Coll Nutr. 2003 Feb;22(1):9-17. PMID 12569110
- DeBruyne L, Pinna K, Whitney E (2011). "Chapter 7: Nutrition in practice — Fad Diets". Nutrition and Diet Therapy. Nutrition and Diet Therapy. Cengage Learning. p. 209. ISBN 1-133-71550-8.
"a fad diet by any other name would still be a fad diet." And the names are legion: the Atkins Diet, the Cheater's Diet, the South Beach Diet, the Zone Diet. Year after year, "new and improved" diets appear ...
- Bijlefeld M, Zoumbaris SK (2014). "Sears, Barry". Encyclopedia of Diet Fads: Understanding Science and Society (2nd ed.). ABC-CLIO. pp. 190–191. ISBN 978-1-61069-760-6.
- Baron M. Fighting obesity Part 1: Review of popular low-carb diets. Health Care Food Nutr Focus. 2004 Oct;21(10):1, 3-6, 11. Review. PMID 15493377
- Baron M. The Zone Diet. Health Care Food Nutr Focus. 2004 Oct;21(10):8-9, 11. PMID 15493380
- Lara-Castro C, Garvey WT. Diet, insulin resistance, and obesity: zoning in on data for Atkins dieters living in South Beach. J Clin Endocrinol Metab. 2004 Sep;89(9):4197-205. PMID 15356006