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Friday July 20 2018

An evaluation of low-carb diets: Fad or fact?

The Atkins diet has emerged in recent years as a serious contender among diets. Rising above many other fad diets by allowing its adherents to eat the fat-heavy foods that most other diets forbid, low-carb diets have reached a serious level of popularity. Although its advocates swear by it, diets like the Atkins run counter to much conventional wisdom, making many skeptical of its purported benefits and wary of its potential risks.

The Atkins diet is the most well-known example of a low-carbohydrate diet, first introduced in 1998 by Dr. Atkins in his book Dr. Atkins’ New Diet Revolution. Theoretically, low-carb diets would force the body into ketogenesis. In such a state, the body metabolizes fats instead of stored sugar, with ketone bodies serving as the body’s energy currency instead of glucose. By forcing the body into this state of fat metabolism, proponents of the Atkins diet argue that weight loss is made easier. Additionally, ketone bodies are also thought to suppress hunger and increase feelings of satiety.[1]

Many in the scientific community, however, disagree on the true effects of low-carb diets. Reviews published by prominent researchers in the field of nutritional health vary in opinion from wholehearted support to skepticism in favour of more conventional diet recommendations.[2] [3] This is further complicated by how researchers advocating for more moderate positions also often do so in part to promote their own favoured diet – oftentimes an intermediary between low-carb and conventional low-fat.[4]

It does not help that the marketplace for diets has become overladen with information. Options for diets abound and every health show or celebrity seems to endorse their own fad weight loss program over all others. Add onto this anecdotal tales spread by media and word-of-mouth – perhaps invoking the mysterious term “metabolism” or appealing to a diet’s supposedly natural origins – and you have the recipe for a convoluted, confused mess. In the modern age, it is an overabundance of information – especially unreliable information – rather than a lack of information that is most harmful to the everyday consumer.

In an effort to address this confusion, many systematic reviews have been published, questioning the efficacy of low-carb diets from an evidence-based perspective. One such systematic review, published in the Journal of the American Medical Association in 2014, found that low-carb diets resulted in the most weight lost after 6 months out of all the diets studied, and the second-most after 12 months.[5] This would seem to suggest that low-carb diets are good for short-term weight loss and satisfactory for weight loss in the long-term – a position promoted by some scientists.[6]

A closer reading of the data disagrees with such a straightforward conclusion. In absolute terms, all diets studied performed similarly. At 6 months, low-carb diets only resulted in 0.71 kg more weight lost than its closest competitor. At 12 months, it lost out to low-fat diets by an average of only 20 grams. Such differences are quite small and, considering variation within study samples, not very significant to any individual reader. Nutrition research is also notoriously difficult to carry out. Scientists cannot maintain total control over their subjects’ diets – food is available everywhere after all – and rates of attrition in studies of restrictive diets are high. Simple, definitive conclusions should be taken with a grain of salt.

Furthermore, the effectiveness of low-carb diets in causing weight loss is not the only important health outcome. Those on ketogenic diets will often be compelled to take multivitamins, due to imbalances in their diet.[7] Another oft-noted side-effect of low-carb diets has been constipation, because of low dietary fibre. Researchers also suspect that consuming high levels of protein increases the burden on the kidneys, which may exacerbate existing renal conditions but does not appear to cause the development of such conditions in the unafflicted.[8] Overall, there is little evidence to suggest that low-carb diets are associated with serious adverse health outcomes.

Ultimately, despite the disagreements in the literature, it seems as though low-carb diets are neither the unnatural evil that its detractors paint it as, nor the silver bullet for weight loss that its supporters believe it to be. In the simplest terms, weight loss is dependent on an energy deficit – spending more calories than eaten. The easiest way to achieve this is calorie restriction. It is certainly possible that different diet compositions may influence metabolism, but the data currently available tends to indicate that the specific diet chosen matters less than sustained commitment to reducing the number of calories consumed.


References: 

[1] Acheson KJ. Carbohydrate and weight control: where do we stand? Curr Opin Clin Nutr Metab Care 2004;7(4):485-92. Available from: https://www.ncbi.nlm.nih.gov/pubmed/15192454

[2] Denke MA. Metabolic Effects of High-Protein, Low-Carbohydrate Diets. American Journal of Cardiology 2001;88:59-61. Available from: https://www.ncbi.nlm.nih.gov/pubmed/11423059

[3] Astrup A, Larsen TM, Harper A. Atkins and other low-carbohydrate diets: hoax or an effective tool for weight loss? Lancet 2004;364:897-99. DOI: 10.1016/S0140-6736(04)16986-9

[4] Walker C, Reamy BV. Diets for cardiovascular disease prevention: what is the evidence? Am Fam Physician 2009;79(7):571-8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19378874

[5] Johnston BC, Kanters S, Bandayrel K, et al. Comparison of Weight Loss Among Named Diet Programs in Overweight and Obese Adults. JAMA 2014;312(9):923-933. DOI: 10.1001/jama.2014.10397

[6] Clifton P. The science behind weight loss diets. Aust Fam Physician 2006;35(8):580-2. Available from: https://www.ncbi.nlm.nih.gov/pubmed/16894429

[7] Pickering TG. Diet Wars: From Atkins to the Zone. Who Is Right? J Clin Hypertens 2002;4(2):130-3. Available from: https://www.ncbi.nlm.nih.gov/pubmed/11927796

[8] Knight EL, Stampfer MJ, Hankinson SE, et al.  The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med 2003;138(6):460-7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/12639078

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The Meducator is McMaster University’s undergraduate Health Sciences Journal. It publishes pieces that critically address current issues with a high degree of scientific rigor, but in a way that is accessible to a broad audience.

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