Sugar, carbohydrates, exercise and obesity – Expert reaction

US and South African scientists question whether we can overcome an unhealthy diet through exercise alone.

Credit: Flickr/Robert Anthony Provost

In an editorial in the British Journal of Sports Medicine, the experts say they believe excess sugar and carbohydrates – not a lack of exercise – lie behind the surge in obesity.

Our colleagues at the Australian and UK SMCs have collected the following expert commentary. Feel free to use these quotes in your stories. If you would like to speak to a New Zealand expert, please contact the SMC (04 499 5476;

Professor Manny Noakes, Research Director for Nutrition and Health at CSIRO, comments:

“It is a complete myth that sugar and carbohydrate alone are solely responsible for obesity. Australians eat over 30 per cent of excess kilojoules from indulgence foods. Some may be high in sugar and carbohydrate, but many may also be high in fat and salt.

“Eating for good health and wellbeing will not be achieved by focussing on avoidance of one nutrient. The failure of low fat foods will be repeated with low sugar and carbohydrate foods unless we focus on balanced nutrition. Exercise has many benefits, but particularly for weight loss maintenance rather than weight loss.”

Dr Tom Wycherley, Postdoctoral Research Fellow in the School of Population Health at the University of South Australia, comments:

“The authors correctly highlight that regular exercise participation has many associated benefits that include reducing the risk of developing cardiovascular disease, type 2 diabetes, dementia and some cancers. For these and a growing list of other reasons it is, and should continue to be, strongly endorsed. Nevertheless, as a tool for actually reducing bodyweight exercise is a reasonably inefficient method. Rather, for most people the key mediator of weight loss is caloric intake.*(see endnote)

“The role of exercise in prevention of weight gain may perhaps be more substantial; one of the most common characteristics of people that have maintained a weight loss long term is that they participate in regular physical activity. However, at a population level, minimising excess calorie intake is certainly a key consideration for prevention of obesity.

“Avoiding foods and drinks that are high in added sugar may represent a sensible strategy to avoid surplus calorie intake and adverse cardio-metabolic effects without compromising the nutritional quality of the diet. Specifically, foods and drinks that are high in added sugar (especially water-based sugar-sweetened beverages) often supply calories without contributing key nutrients or inducing a feeling of fullness. Hence they are essentially ’empty calories’ that can promote surplus energy intake that leads to weight (body fat) gain and increased risk of type 2 diabetes and cardiovascular disease.

“Modifying the food environment to facilitate making healthy choices is an excellent, albeit extremely complex, notion.”

*For most people it is simply not realistic to expect to achieve notable weight reduction through exercise alone. There is a useful online tool by the NIH that can be used to reasonably predict individual weight changes in response to diet and exercise interventions.

Dr Alan Barclay, Practicing Dietitian and Nutritionist, Chief Scientific Officer at the Glycemic Index Foundation, and Head of Research at the Australian Diabetes Council, comments:

“This opinion piece by low carbohydrate activists hypothesises that carbohydrates in general, and sugars in particular, are the primary drivers of obesity and associated chronic diseases such as type 2 diabetes, and infer that rising levels of physical inactivity, as seen in Australia, are not contributing factors.

“While there is evidence that overconsumption of refined carbohydrates (particularly those with a high glycemic load) may increase the risk of obesity and type 2 diabetes, refined fats, proteins and alcohol also provide unwanted kilojoules in most people’s diets and should not be overlooked.

“The recent WHO-endorsed systematic review of dietary sugars and body weight determined that: “Among free living people involving ad libitum diets, intake of free sugars or sugar sweetened beverages is a determinant of body weight. The change in body fatness that occurs with modifying intakes seems to be mediated via changes in energy intakes, since isoenergetic exchange of sugars with other carbohydrates was not associated with weight change.” Also, a recent systematic review of observational studies did not find any compelling evidence linking sugar consumption to type 2 diabetes risk, with the exception of sugar sweetened beverages.

“This evidence is more powerful than the cross-sectional ecological study referred to in the opinion piece. In considering these data, it’s important to remember that relative risks (RR) for smoking and chronic disease are very high (50 +), whereas the RRs for carbohydrate and chronic disease are typically 1.2-1.5, so it is not helpful to equate carbohydrates with tobacco.”

Jane Martin,  Executive Manager of the Obesity Policy Coalition (OPC) and of Alcohol and Obesity Policy at Cancer Council Victoria, comments:

“This exciting new research is further evidence of the significant role highly processed food plays in our battle with obesity. In Australia these ‘extra’ foods make up a large part of our diets – almost half for adults and around one-third for children – and many of these foods are rich in carbohydrates and contain high levels of added sugar.

“By showing that you can’t outrun a bad diet, this research flies in the face of food giants such as Coca Cola who are positioning themselves as part of the solution, telling consumers that managing weight is all about getting the energy balance right.

“We won’t solve our obesity problem with physical activity alone. We also won’t solve the issue by simply telling people what to do.

“To bring about change in our diets and really address our weight problem we need a comprehensive approach involving all levels of government and community.

“We need strong policies, such as restricting junk food marketing to children, regulating the quality and availability of food in school settings, taxing sugar-sweetened beverages, mass media campaigns, and placing the health stars on the front of packaging among others.”

Bill Shrapnel, Dietitian and Nutritionist and runs a website called the Sceptical Nutritionist, comments:

“This paper is not based on new research. It is an opinion piece published in a lowly journal. The authors are renowned for their unconventional views.

“The paper appears to be made-for-public relations, with the usual overstatement and demonisation of the food industry. But the arguments are poorly developed and misleading. For example, it is argued that the message to maintain a healthy weight through calorie control is a ‘false impression rooted in the Food Industry’s Public Relations machinery’. Rather, it’s the position advocated by all reputable nutrition and obesity organisations in the world.

“Some of the claims in the paper are simply wrong. For example, it is claimed that sugar calories promote hunger and fat calories promote fullness. However, studies directly comparing the effects of sugars and fats on satiety find there is little difference between the two. Protein is more satiating than both.

“The paper claims that a recent study found that every excess 150g of sugar is associated with an eleven-fold increase in the prevalence of diabetes. The study actually found that every excess 150g of sugar is associated with a 1.1 per cent increase in the prevalence of diabetes. [Basu S., et al, 2013]. Even then, the study is of poor quality, highlighted by the extensive limitations listed in the Discussion.

“I don’t understand why these authors would attempt to undermine recommendations for increased physical activity from an expert group. Both diet and exercise are important – it’s not a matter of one or the other.

“This paper makes no useful contribution to the debate about the best means of addressing the twin epidemics of obesity and type 2 diabetes.”

Declared interests: Bill Shrapnel is a member of the Sugar Research Advisory Service.

Dr Joanna McMillan, Nutritionist, Accredited Practising Dietitian and Sports Dietitian, comments:

“I agree entirely that you ‘cannot outrun a bad diet’ but it is essential that we don’t turn Australians away from exercise and activity. There is no doubt that we are less active than we were in previous generations and that this is part of the aetiology of weight gain over the years. Exercise may not be a route to weight loss in the short term, but it does have an important role in preventing weight gain and maintaining weight loss. Then, as the authors point out, there are numerous other health benefits to being more active. The bottom line is that, even in the absence of weight loss, being metabolically fit through regular exercise is essential for a well-functioning body – arguably more important than losing weight, and is crucial in the management and prevention of type 2 diabetes.

“I do think we need more careful advice given to distinguish athletes from the everyday exerciser or ‘weekend warrior’. I agree with the authors that the legitimisation of certain products, including sports drinks, by their endorsements and associations with sport, needs to stop. People need to understand that what an athlete in vigorous training requires is not the same as the rest of us when we do an hour session in the gym, or go for a half hour run. For athletes however, while some may well perform well on high fat low carb diets (as S Phinney has shown in his group’s own studies) others have not found the same results. It may well depend on the specifics of the sport but there is an abundance of evidence showing that high carbohydrate diets improve performance. I would direct journalists to Prof Louise Burke at the AIS for information on this.

“Finally yes let’s make healthy the easy choice! How we do that is the question. Pointing the finger of blame at sugar, or carbs in general, and then replacing with a myriad of highly processed low carb products only repeats the mistakes of the past. We must move towards a more whole food diet to incorporate all we know about good nutrition. Wholegrains, legumes and whole fruit – all carb-rich foods – have many health benefits – including being major sources of fibre and phytonutrients – and cannot be put in the same basket as soft drinks, lollies, cakes and so on. Currently, Australians, on average, obtain more than a third of their kilojoules from these discretionary food sources – let’s concentrate on reducing consumption of these and we will go a lot further in reducing overweight and obesity rates than demonising carbs.”

UK SMC comments:

Prof Iain Broom, Director, Centre for Obesity Research and Epidemiology, Robert Gordon University, Aberdeen, comments:

“In general this editorial is similar to that of Richard Smith in the Christmas edition of the BMJ. I would tend to agree that high CHO diets tend to exacerbate insulin resistance syndrome and are really not appropriate in dealing with the metabolic problems associated with this syndrome, despite the fact they are classified by Public Health as the healthy approach to weight management. Low CHO diets are associated with much greater improvement in insulin sensitivity than low fat approaches in individuals with metabolic syndrome and this has been well documented since the 1970s.

“There are one or two misconceptions in this editorial, especially related to the satiety aspects of macroniutrients. Fat has the least satiety effect, followed by CHO and then protein and not as the authors suggest.

“Their statement that increased exercise does not contribute to weight loss is well taken – it does not. What exercise (increased activity) does, in association with appropriate dietary intervention, is to promote weight loss maintenance once weight has been lost, but it is a poor contributory factor to promoting weight loss. What is good about this editorial is that it once again focuses attention on what Richard Smith described as a global experiment in changes in food policy which has gone disastrously wrong. Public Health, unfortunately, has little experience in dealing with the obesity/diabetes epidemic worldwide and is using the wrong food.”

Ms Catherine Collins, Spokesperson for The British Dietetic Association, comments:

“Anyone who’s spent time at the gym on a treadmill will have realised just how much effort is needed to burn off the calories in an average bar of chocolate. But this personal opinion piece, which extolls the purported benefits of a high-fat low-carb diet, doesn’t given sufficient recognition to the extensive research of the metabolic and physical benefits to health of even moderate intensity exercise.

“As a Registered Dietitian, seeing incomplete evidence being cited so frequently is a worrying trend in medical publications. When it comes to information on diet, exercise and health the public deserve robust, well-evidenced recommendations, which this paper fails to deliver.

“The poor interpretation of evidence cited to support the article should also be addressed. The authors state that ‘up to 40% of those with normal BMI will harbour metabolic abnormalities…’ citing a reference that did not generate this point (i).

“In my opinion there are a mere two valid points made in this opinion piece. First, that the UK Academy of Medical Royal Colleges statement on the benefits of exercise – in terms of heart health and metabolic risk – is proven. In addition to burning up a modest calorie load, exercise also improves mood, so reducing your urge to achieve the same feeling with a calorie-laden bar of chocolate. Second, sports centres should prioritise sugar-free beverages at point of sale to recreational sportsmen and women, who if overweight don’t need isotonic and other sugary drinks to rehydrate. Water will do.”

(i) Reference 3 in the paper refers to this paper co-authored by Lustig. It is used to cite a 40% incidence of metabolic syndrome. However, the Lustig paper makes no such claim. The 40% incidence arises from their citing reference 18 (PMID: 219202630) of their paper. Reference 18 is the excellent paper from Voulgari and colleagues Voulgari’s work (table 2) demonstrates a statistically significant reduction in heart failure risk with any level of exercise intensity. Whether exercise protects against heart failure, or that lack of ability to participate of exercise is a symptom of heart failure risk, is not qualified.

Declared interests: “I have been paid to present a talk on my personal interpretation of dietary guidelines on sugar to a group of dietitians, by a company that manufactures a fruit juice.”

Prof Nick Finer, Honorary Professor, National Centre for Cardiovascular Prevention and Outcomes, UCL Institute of Cardiovascular Science, UCL, comments:

“This polemical article gives punchy messages on the relationships between sugar(s), physical activity, obesity and ill health. While many of the messages are valid and important in places the authors overstate their case. They set up many Aunt Sallies that they then proceed to knock down. Disappointingly they do not reference two recent important reports from the UK. The National Institute for Health and Care Excellence (NICE) report (Maintaining a Healthy Weight and preventing excess weight gain among children and adults – NICE NG7, published in March 2015) and the draft report on carbohydrates and health from the Scientific Advisory Committee on Nutrition from June 2014 systematically reviewed this area of huge public health importance.

“The authors correctly highlight that a ‘normal’ body mass index (presumably they mean between 18.5 and 25 kg/m2) may not be healthy, but then rather confusingly conflate a number of themes into the statement that ‘…members of the public are drowned by an unhelpful message about maintaining a ‘healthy weight’ through calorie counting, and many still wrongly believe that obesity is entirely due to lack of exercise.’ Actually public health messages more commonly talk about a healthy diet and the benefits of remaining physically active. The NICE NG7 guideline recommends that people ‘establish and maintain a combination of increased physical activity and healthier dietary habits to achieve and maintain energy balance’. There is no mention of calorie counting or obesity being entirely due to inadequate exercise.

“In their simplification of the evidence they frequently confound evidence of association with causation. Many would not accept the statement that ‘an 11-fold increase in the prevalence of type 2 diabetes, in comparison to an identical 150 calories obtained from fat or protein’ is evidence of sugar causing diabetes. In fact the SACN report specifically states that there is no evidence for sugars or sucrose intake in general and type 2 diabetes (based upon limited evidence, 6.21; 6.27) but does recognize that in the case of sugar-sweetened beverages specifically, there is moderate evidence for a biologically important association with higher diabetes incidence (6.35). The impact on weight of children exposed to sugar-sweetened beverages, while not specifically mentioned, is perhaps more strongly evidenced.

“The article is on much firmer ground in highlighting and debunking the carefully contrived marketing-speak that promulgates the need for ‘sports drinks’, carbohydrate loading and insidiously suggests that, often small, bouts of exercise can legitimise consumption of sugar-laden beverages without caloric penalty. This article is a timely stab back at industry-created myths relating to exercise, sugars and obesity that seek to drive up the unnecessary consumption of their unneeded products.”

Prof Susan Jebb, Professor of Diet and Population Health, University of Oxford, comments:

“It is true that the magnitude of weight loss following exercise-only interventions is less than that achieved in diet-only interventions as we showed in a systematic review and meta-analysis last year (Johns, Hartmann-Boyce, Jebb and Aveyard. J Acad Nutr Diet. 2014 Oct;114(10):1557-68). But in this editorial, the authors fail to note that weight loss programmes which combine diet and physical activity are the most successful route to weight loss in both the short (3-6 months) and medium term (12 months). Moreover, to constrain the intention behind efforts to treat obesity to achieving weight loss alone neglects the true purpose of intervention – to improve health. Given that obesity, an unhealthy diet and physical inactivity are all risk factors for chronic disease, it makes good sense to seek to change both diet and activity behaviours to lose weight and improve health.

“To achieve this will need a raft of changes at all levels: practical support for individuals to change their behaviour, changes in local environments to both support better food choices and greater physical activity; and some national policy action too. None of these interventions alone will solve the problem, indeed they are very likely to be synergistic. Rather than trade one off against the other – sugar vs fat, diet vs activity, individual vs population we need to take action across the full range. This was the system-wide approach advocated by the Foresight report “Tackling Obesities: Future Choices” in 2007 and which still provides a framework for comprehensive action now.”

Declared interests: Prof Susan Jebb is employed by the University of Oxford and receives no personal funding from the food industry. Susan is the independent Chair of the Public Health Responsibility Deal Food Network and was a science advisor to the Foresight obesity report. From 2007-10 she was the principal investigator for a research study funded by the food industry to investigate the potential for a functional beverage to help weight loss. The results of this work have been published.

Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, comments:

“Whilst this article is provocative and includes many points of merit, with which many of us agree, there are some useful clarifications. There is certainly more evidence to support excess calorie intake as more relevant to the obesity epidemic than under activity. This statement makes sense if one considers how quickly you can eat 200 calories in the form of a calorie-dense snack (e.g. chocolate bar, crisps etc.) as opposed to burning off 200 calories. Thus the main point of the article that one cannot outrun a bad diet is true for the vast majority of the population. However, we must remember that physical activity, whatever its form, is important in preventing weight gain and helps the heart and thus both a good diet and good activity levels are important for healthy weight and general health.

“Whilst excess sugar often contributes to excess calorie intake for many individuals, fat excess is also important and many individuals are obese due to too much of both dietary sugar and fat. Likewise, there is no convincing evidence from recent high quality intervention trials for an important effect of specific diet types on risk for obesity – what matters more than anything else is overall calorie content. This also makes sense unless we wish to reinvent the laws of physics. But once again, the main sentiment about cutting average sugar or fat intakes and the power of advertising are well made in this article, as in many others. Whether a new government really has the appetite to tackle such issues via legislation targeting at foods and drinks industries or taxation measures remains to be seen.

“Irrespective of the above, in clinical practice we can help our patients who are overweight and obese and who wish to lose weight by giving them one to two realistic targets (e.g. replace sugary drinks with diet drinks or better water, or replace sugary rich cereal with fibre rich cereal, or else replace crisp snacks with piece of fruit etc.) to aim to cut their calorie intake. Most will need additional changes (so more targets subsequently) but as long as changes are embedded and achievable (and palates retrained), we will have made some helpful suggestions and our patients will be thankful.”