Page Content: A recent study by SU researchers on low carbohydrate diets, published in the online journal, PLOS ONE, has sparked a media debate. Prof Tim Noakes responded to the findings of the systemic review in a letter to the Cape Times (scroll down)
Click here for the press release by Stellenbosch University: "Low carbohydrate diets result in similar weight losses to recommended balanced diets. Findings debunk claims that low carbohydrates diets results in more weight loss."
Click here to read the full article published in PLOS ONE
The Author's response to Prof Tim Noakes' letter in the Cape Times, 11/07/2014
Letter to the Editor, Cape Times, 14 July 2014
Trial not high in sugar
We refer to the letter from Prof Tim Noakes that appeared in the Cape Times on 11 July 2014, pertaining to our systematic review published in the international, peer-reviewed journal, PLOS ONE. For the sake of clarity we wish to correct a number of points.
First, the carbohydrate intake prescribed in the low carbohydrate diets in the systematic review ranged from 19 to 192 grams per day across the 19 included trials, and not "a minimum of 200 grams" as stated by Noakes. The levels of carbohydrate in the trials are similar to those recommended on the diet website that Noakes endorses (originaleating.org). The balanced diets in the trials in our systematic review were not high in sugar as implied by Noakes.
Second, the accusations of bias and his claims that we were "ignorant" of existing systematic reviews are unfounded. Before embarking on our study, we examined all previous systematic reviews on the topic and report our overview of these in the background of our scientific publication. We found that many had not considered energy intake (calories) when comparing effects of diets on weight loss and that inconsistent definitions had been used for low carbohydrate and comparison diets. In our review, we clearly defined the low carbohydrate and recommended balanced diets, and included only studies that met these criteria. We also specifically evaluated whether the actual mix of carbohydrates, fat and protein in a diet influence weight loss, independent of the energy intake. We found that, in overweight and obese people, the two diets have similar effects on weight loss and indicators of heart disease risk and diabetes. This was over a two year period, and the same results were seen in overweight and obese people with and without diabetes.
Third, to dismiss a total weight loss of 10 to 12 kg over 3 to 6 months as a "diet failure" as Noakes has done is unreasonable. Research shows meaningful changes in risk factors, such as blood pressure, with a weight loss as little as 2.5 kg, or 2% of body weight.
Fourth, there is no dispute that a key part of the dietary management of diabetes is controlling and at times reducing portions of carbohydrate-rich foods and guiding carbohydrate quality to help with better blood sugar and insulin control. This has been standard dietetic practice for many years and is also commonly known as 'carb counting'. However, this does not involve drastically reducing or eliminating all carbohydrate-rich foods such as cereals, grains and fruit and replacing these foods with large amounts of saturated fats.
Finally, the causes of the increasing burden of obesity are complex and it is an oversimplification to blame it on a single nutrient. Risk factors that contribute to obesity include a combination of genetic, socioeconomic, metabolic and behavioural factors. Significantly, over the past 3 to 4 decades, ultra-processed, energy-dense, relatively cheap food products, high in unhealthy types of fat, added sugar and sodium have been aggressively promoted and are now dominating our food system. Focussing on the manipulation of a single nutrient for weight loss as Noakes recommends does little to help us understand the best ways to treat the serious problem of obesity, and misleads and confuses the public regarding weight management. Our research, summarising available carefully conducted scientific trials, shows weight loss with recommended balanced diets is similar to weight loss with low carbohydrate diets. The challenge for us all is to help prevent obesity developing, and to assist those who are overweight and obese with safe lifestyle and dietary changes that help them lose weight and sustain their weight loss.
Yours sincerely
Dr Celeste Naude, Centre for Evidence-based Health Care, Stellenbosch University
Prof Jimmy Volmink, Centre for Evidence-based Health Care, Stellenbosch University, and South African Cochrane Centre, South African Medical Research Council
Prof Paul Garner, Effective Health Care Research Consortium, Liverpool School of Tropical Medicine
Prof Taryn Young, Centre for Evidence-based Health Care, Stellenbosch University, and South African Cochrane Centre, South African Medical Research Council
Prof Marjanne Senekal, Division of Human Nutrition, University of Cape Town
Ms Anel Schoonees, Centre for Evidence-based Health Care, Stellenbosch University
Letters by Prof Tim Noakes
Below are the letters by Professor Tim Noakes to the editor of the Cape Times,
Low-fat, high-carb, high-sugar diet a likely cause of obesity/diabetes (11/07/2014), in response to the study; and
Diet not the real meal (15/07/2014) in response to the above letter by the authors.
Letter to the Editor, Cape Times (11/07/2014)
Low-fat, high-carb, high-sugar diet a likely cause of obesity/diabetes
I refer to the report in the Cape Times of July 10, "Noakes's popular low-carb diet is not healthier, better for weight loss - study ". Since the authors of that study do not undersatnd either what constitutes a low-carbohydrate diet or the unique biological effects of such diets, they were predisposed to produce a biased report that comes to exactly the wrong conclusion.
First, the conclusion of their study was predictable since the authors chose to review only studies in which subjects ate the same number of calories on both diets. It is not clear how the authors conceived that diets that provided exactly the same number of calories would produce different outcomes. Indeed, a core teaching of these nutritional scientists is that the degree of weight loss is determined by the reduction in calorie consumption. Thus the authors knew the outcome of their study even before they undertook it. This is not good science.
Second, the studies included in their meta-analysis are not of the low-carbohydrate diet described by either Dr Robert Atkins or ourselves in Real Meal Revolution. Dr Atkins realised in the 1970s that the majority of overweight/obese persons can only reduce their weights successfully, and keep that weight off in the long term, if they eat less than 60g carbohydrate/day for the rest of their lives. Higher intakes are increasingly less effective. In Real Meal Revolution we stress that those with insulin resistance/ type 2 diabetes need to keep their carbohydrate intakes even lower, ideally to about 25g/day. The "low-carbohydrate " diets included in the meta-analysis provided a minimum of 200g carbohydrate/day (or 4-8 times higher than the carbohydrate content that is known to be effective). As a result this is a meta-analysis of studies providing a high, not a low-carbohydrate load for those with obesity/insulin resistance/type 2 diabetes.
Third, the extent of weight loss in the studies included in he meta-analysis is small, the greatest values being about 10kg. For most people with significant weight problems, such small weight losses are probably relatively meaningless and should be classified a diet failure, not a success. But freeliving persons who follow individually prescribed carbohydrate diets providing about 25g carbohydrate/day report quite remarkable degrees of weight loss, not infrequently up to 40-80kg, usually achieved effortlessly if the low-carbohydrate rules are followed.
Fourth, the unique biological effects of the properly-defined low-carbohydrate is that (i) It reduces hunger, allowing subjects to eat fewer calories without experiencing continual hunger. The point, as stressed by Dr Atkins, is that the low-carbohydrate diet is a low-calorie, no-hunger diet. (ii) The diet lowers blood insulin concentrations. In those with obesity/insulin resistance/metabolic syndrome, it is continually elevated blood insulin concentrations that cause ill-health (as clearly established by the work of Dr Gerald Reaven of Stanford University over the past 50 years).
The authors found that their study found that health benefits were no different on either diet.
A number of properly designed, peer-reviewed meta-analyses of the real low-carbohydrate diets show that weight loss and health benefits are superior compared with higher-carbohydrate diets.
Unfortunately, the authors appear to be ignorant of those studies since neither they nor your reporter refers to them. This implies the presence of bias, questioning the true intent of the report.
The report also includes the statement of the Heart Foundation of South Africa (HFSA) to the effect that a diet high in saturated fat causes heart disease. Unfortunately, the HFSA spokesperson appears unaware of Nina Teicholz's recently released book, The Big Fat Surprise: Why Butter, Meat and Cheese Belong in a Healthy Diet, and the recent Time Magazine (June 23), which show that this dogma is false and is not based on any credible science. It is perhaps time that the HFSA updated its understanding of what actually causes heart disease. They might also want to consider whether their promotion of their unproven low-fat, high-carbohydrate, high sugar diet for the past 37 years is the most likely direct cause of the obesity/diabetes epidemic that has since engulfed South Africans.
Indeed on a practical side, I wonder if the authors have ever considered studying the dietary intakes of the obese diabetic patients they treat at Tygerberg and Groote Schuur hostpitals. Do patients with these diseases eat either high- or low-carbohydrate diets? Why is is that these twin diseases, which are crippling the health services of the Western Cape, began to increase exponentially only after the 1977 Dietary Guidelines that institutionalised the low-fat, high-carbohydrate diets? Surely these are the critical questions that should really be exercising the minds of the Western Cape's nutritional scientists?
The best conclusion that can be drawn from this study is that diets providing more than 10 percent of daily calories in the form of carbohydrate are equally ineffective in producing meaningful degrees of weight loss in those with obesity/insulin resistance/type 2 diabetes.
Professor Tim Noakes
Sports Science Institute of South Africa
Newlands
Letter to the editor, Cape Times (15/07/2014).
Diet not the real meal
The response of Dr Celeste Naude and colleagues ("Trial not high in sugar," Cape Times letters, July 14) to my letter confirms my point. The authors definition of a "low" carbohydrate diet was one that included up to 192g carbohydrate a day whereas the upper limit of carbohydrate intake that is known to be effective in persons with diabetes/obesity/insulin resistance is 25-50g a day.
Thus their analysis was not of low carbohydrate diets as defined in The Real Meal Revolution and elsewhere. When meta-analyses of properly defined low-carbohydrate diets are undertaken they show that weight loss and metabolic changes are superior on carbohydrate diets providing less than 50g a day than they are on higher carbohydrate intake (Beuno NB et al. Br J Nutr 2013; 110: 1178-87), disproving the conclusions of Dr Naude and her colleagues.
Professor Timothy Noakes
Sports Science Institute of South Africa
Newlands