Evidence-based comments on high-protein and low-carbohydrate diets

High-protein (HP) low-carbohydrate (LC)diets: Evidence based comments

A/Prof M Senekal PhD, RD(SA), Division of Human Nutrition, Department of Human Biology

Faculty of Health Sciences, University of Cape Town

Do HP-LC diets result in better weight loss, blood lipid andglucose levels than conventional diets(higher carbohydrate, lower protein, low fat)?

Research shows that HP-LC diets may result in more weight loss and better improvements in blood lipid and glucose levels when compared at 6 months than conventional diets. However, when compared at 12 and 24 months, these differences disappear. Researchers conclude that a consistent reduction in total energy intake,rather than changing carbohydrate (CHO), protein and fat contributions to total energy intake,is key to successfulweight lossand associated benefits.

THUS,THERE ARE NO SUPERIOR BENEFITS RESULTING FROM HP-LC DIETS

Concerns about HP-LC diets

The HP-LC diet approach oftendisregards all the other risks for obesity and chronic disease. These risks includeunknown genetic variation, physical activity, smoking and excessive alcohol intake.

There is no agreement on how much protein and how little CHO would constitute a HP-LC diet, both in research as well as among popular versions of HP-LC diets.

The HP-LC diet proponents negate core nutrition principles, including:

The need to includea varietyof foods in your diet;
The need for CHO in the form of fruits, vegetables, unrefined cereals and legumes in your diet to provide sufficient intake of fibre, vitamins and antioxidants;
The importance of selecting no-fat/low-fat options of animal proteinfoods to reduce total and especially saturated fat intake;
The importance of reducingsaturated and trans-fatintake, and replacing it with monounsaturated and polyunsaturated fats, for heart diseaseprevention.
No long-term (post 24 months) evidence is available on the safety of the HP-LC diet

Possible increased risk for the following conditions isa serious concern:

Obesity (if high fat intake persist without reducing total energy intake);
Cardiovascular disease (high saturated fat intake, low antioxidant and fibre intake,excess free iron as a result of high meat intake, which results inincreased levels of free radicals);
Diabetes (whole body insulin resistance, red meat intake, low antioxidant and fibre intake, high total fat intake)
Osteoporosis (increased calcium losses)
Excessive iron stores in genetically susceptible individuals, resulting in damage to various organs.
Other points to remember

Productionof animal proteinfoods has a more negative impact on the environment and is less sustainable than production ofplant foods.

HP-LC diets are only affordable for a privileged few, as it is more expensive than a lower protein, higher CHO diet.

Participants in research on the effect of different weight loss diets found it difficult to stay on any of the diets, with between 20 and 80% dropping out. This underscores the fundamental problem with weight management: people find it very difficult to make drastic changes in their dietspermanently to ensure long-term weight loss and maintenance.

Diets that are popularized in various ways, either by celebrities or the diet industry, often result in the misconception of a “magic bullet” solution, with one diet being claimed tobe the answer for all. This misconception also undermines the truth of the need for permanent dietary (and other life-style e.g. physical activity) changes to ensure long-term healthy weight management.

Finally, the HP-LC diet is not a new concept. It first emerged in the mid 1800s, with an obese (BMI 35) London based undertaker being advised by his physician to cut all sugar and starch from his diet. He went on to lose 24kg, wrote a book on his diet and sold 58000 copies by the time he passed on(what is new?)! Early in the 2000 the Atkins diet once again took the United States by storm, so much so that economic indicators showed that the red meat (beef) and egg industries were experiencing a boom, while the grain industry took a knock. It is interesting to note that by 2004 these indicators returned to pre-2000 levels, with obesity being as big a problem as before.

In conclusion, although HP-LC diets may have short term benefits, no research has been published that sheds light on possible long-term (post 2 years)benefits or dangers. At this stage these diets can thus not be promoted for long-term successful weight loss andhealth.

The general population should focus on following the Food Based Dietary Guidelines (http://www.fao.org/ag/humannutrition/nutritioneducation/fbdg/49849/en/zaf/) for healthy eatingpromoted by the Department of Health. For the individual who considers weight loss for improved health, consultation with a registered dietitian,who will be able to offer appropriate and individualized dietary guidance, is advised.

References

1. Weber CL, Matthews HS. Food-miles and the relative climate impacts of food choices in the United States. Environ Sci Technol, 2008 May 15;42(10):3508-13.

2. Institute of Medicine Food and Nutrition Board. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). Washington, DC: National Academies Press; 2002/2005.

3.World Health Organization/Food and Agricultural Organization. Diet, Nutrition and the Prevention of Chronic Disease. Report of a Joint WHO/FAO Expert Consultation. Chapter 5: Population nutrient intake goals for preventing chronic-diseases. Geneva: World Health Organization 2003.