Thank goodness for the World Health Organization’s new report ‘Sugars intake for adults and children’. Now, at last, we have some actual science to go on.
WHO’s record on sugar
The World Health Organization (WHO) is a leading global health agency with a proud history of sound dietary advice, including advice about sugar. In a 1990 report, WHO recommended a limit on intake of ‘free sugars’ of no more than 10% of daily calories, which is about the current average intake of Australian adults. Free sugars means all sugars added to foods by the manufacturer, cook or consumer, plus sugars in honey, fruit juices and syrups.
WHO’s rationale for limiting sugar intake was to lower the risk for tooth decay. No lower limit on intake of free sugars was recommended.
Thirteen years later WHO again looked at the science of sugar and health and found ‘convincing’ evidence that both the amount of free sugars and the frequency of sugar consumption increased the risk for tooth decay. And again WHO recommended a limit of 10% of daily calories.
The 2015 WHO report
In its latest report WHO found … wait for it … that eating too much sugar causes tooth decay and that the intake of free sugars should be limited to … wait for it … less than 10% of daily calories.
Fructose – the dietary villain de jour – is currently giving rise to more myths than anything else and they all seem to relate to fat. Fructose supposedly leads to fatty liver and too much fat in the blood. To top it off, fructose is said to be uniquely fattening! Where do we start?
Fat in your liver
Most of the carbohydrate we eat ends up in the bloodstream as either glucose or fructose. The myth goes that glucose is the good sugar as it is used to power the brain, the muscles and most of the cells in the body. And the fructose is the bad sugar which is quickly taken up by the liver and turned into fat, giving rise to fatty liver.
Unfortunately for the myth-makers, no reputable health authority in the world agrees. Fatty liver is certainly a common problem but the experts see it as part of the metabolic syndrome – a cluster of abnormalities linked to central obesity and insulin resistance, where the cells of the body become less sensitive to insulin.
There is no recommended diet for fatty liver. Instead, health authorities encourage people with fatty liver to lose some weight and increase their physical activity, both of which improve insulin resistance.
According to advocates of low carbohydrate diets a key benefit is the effect on triglycerides in the blood. The argument goes that a high level of triglycerides is linked to increased risk for coronary heart disease; low carb diets lower triglycerides; so low carb diets should lower the risk for heart disease. Sounds plausible enough, but is it true?
Blood lipids and heart disease risk
The approach to managing blood lipids to lower heart disease risk has evolved over time as our understanding of this complicated field has grown. Decades ago the focus was on lowering total cholesterol but this was later narrowed down to LDL-cholesterol – ‘bad’ cholesterol for the lay person. ‘Good’ HDL-cholesterol was considered protective and the balance between the bad and the good – the LDL/HDL ratio – came into use. More recently, the total cholesterol/HDL ratio has been considered to be a better measure as all non-HDL-cholesterol appears to increase heart disease risk.
What about triglycerides?
If you are interested in how triglycerides affect the risk for heart disease and how diet affects blood triglycerides look no further than the American Heart Association’s scientific statement Triglycerides and Cardiovascular Disease. You may need to allocate an afternoon as the paper is very comprehensive and has over 500 references.
As the focus of public health nutrition switches from fats to carbohydrates there is uncertainty about how carbohydrates actually affect the risk for chronic diseases, such as type 2 diabetes and coronary heart disease. Early dietary advice on fats was based on effects on blood cholesterol but what mechanisms are driving the risk associated with carbohydrate?
Glycaemic response or fructose?
One view is that the key driver of carbohydrate-related risk is glycaemic response i.e. the degree to which carbohydrates raise blood glucose and insulin levels. If glycaemic response is the critical factor then the dietary measure of interest would be glycaemic load, which takes into consideration both the amount of carbohydrate consumed and its potential to raise blood glucose.
An alternative view is that fructose drives the chronic disease risk associated with dietary carbohydrate. If so, we should expect fructose or perhaps sucrose (the major dietary source of fructose) to be associated with risk for chronic disease in large population studies. And, importantly, glycaemic load would not be linked with risk.
Let’s look at the epidemiology and see if it supports one argument or the other.
Glycaemic load and coronary heart disease risk
Four meta-analyses of prospective cohort studies of glycaemic load and risk for coronary heart disease have been published in the last couple of years (Dong 2012, Fan 2012, Ma 2012, Mirrahimi 2012). The findings are essentially the same – glycaemic load is associated with heart disease in women but not men. In two of the meta-analyses the links between glycaemic load and heart disease were stronger in overweight subjects. Fan (2012) also found an association with stroke incidence, as did Sieri (2013) in a recent cohort study. In all four meta-analyses the relative risks for heart disease in men were positive – they just failed to reach statistical significance, perhaps due to smaller numbers.
A study in a Chinese cohort published last year found glycaemic load was associated with coronary heart disease risk in both genders (Yu 2013). Compared to studies in western populations carbohydrate intake was high (68% of calories) but sugar intake was relatively low. Most of the carbohydrate was starch, 87% of which came from white rice and refined wheat products.
Over the last year or so two senior Australian nutritionists have been subjected to a sustained social media campaign to denigrate them and their research. Their alleged crime? Daring to say what they believed to be true.
In 2011, Professor Jennie Brand-Miller from the University of Sydney and Dr Alan Barclay, Chief Scientific Officer at the Glycaemic Index Foundation and Head of Research at the Australian Diabetes Council published a paper on the Australian Paradox – the apparent fall in sugar consumption that occurred over a period when rates of obesity in this country increased. The paper was obviously intended to stir the pot a little.
The narrative in the United States at the time was that the increase in obesity prevalence in that country had coincided with increasing sugar intake, so perhaps sugar was a causative factor. In their paper Barclay and Brand-Miller pointed out that while that may well be the case in the United States, sugar intakes had remained fairly constant in the United Kingdom over the same period and had actually fallen by 16 per cent in Australia. However, both countries had experienced an increase in rates of obesity, hence the Australian Paradox.
Under normal circumstances this simple paper may have dissolved away into the vast ocean of scientific literature and never been heard of again. However, a member of the public took exception to the finding that sugar intakes in Australia were falling. Despite not having any qualifications in nutrition or science he had formed a view that sugar intakes in Australia were in fact rising. A social media campaign was initiated to attack the nutrition researchers and their findings and a formal complaint was lodged with the University of Sydney.
“The problem is that many dietitians around the world are telling people to have wholegrain bread when most wholegrain bread is roughly comparable to eating a bag of glucose.”
Last month Professor Jim Mann** addressed the annual conference of the European Association for the Study of Diabetes (EASD) in Barcelona on the controversial topic of carbohydrate quality. Although he was mainly talking about carbohydrates in the diets of people with diabetes, what’s good for this group is good for most of us.
Given the current hysteria about sugar it was interesting that Professor Mann had little to say about it. He indicated that the current EASD recommendation for the general population i.e. that total free sugars be limited to 10% of energy, was appropriate and was likely to be retained when new EASD guidelines are released. He had a lot more to say about starch.
Canadian professor Tom Wolever has provided a spirited argument for the adoption of glycaemic index as a measure of carbohydrate quality, lining it up against wholegrains. Which approach should be preferred?
Those who have been following the carbohydrate quality debate will enjoy a recent feisty review by Professor Tom Wolever from the University of Toronto published in the European Journal of Clinical Nutrition. Wolever is the co-inventor of the glycaemic index concept and is obviously a little peeved that other measures of carbohydrate quality such as wholegrain have gained acceptance in dietary guidelines whereas GI has not.
Wholegrains versus GI
Here is how Wolever weighs up the relative merits of wholegrains and GI as measures of carbohydrate quality (minimally edited).
I concluded my presentation at the recent ILSI carbohydrate symposium by stating that sugar content is a poor measure of the nutritional quality of a carbohydrate-rich food. Here is a summary of the argument presented.
Discriminating between carbohydrate-rich foods
To illustrate the argument I used the model for discriminating between carbohydrate-rich foods developed by Professor Manny Noakes and myself. For more information on this model please refer to my previous post or the published paper.
In brief, the model is based on nutrient density and glycaemic index (GI). Nutrient density was chosen as it reflects the fundamental nutritional role of foods – the delivery of essential nutrients. And GI was chosen because it relates to the physiological effect of the carbohydrate itself. When carbohydrate-rich foods are run through the model they end up in one of four carbohydrate quality quadrants.
Carbohydrates were put under the microscope in Sydney last week in a symposium organised by the International Life Sciences Institute (ILSI). The risks and benefits of carbohydrate intake were widely discussed. Here is a taste of what we heard, some observations and a few key references.
Recommended carbohydrate intakes
A couple of speakers discussed the recommended range for carbohydrate intakes, which is 45-65% of daily calories in both Australia and the United States. In the United States, the major factor that determined the upper boundary of intake was adverse effects of carbohydrate on levels of triglycerides and HDL-cholesterol in the blood. At the lower end of the scale it was argued that fibre requirements are unlikely to be met at intakes of carbohydrate below 45% of energy (in the low fibre US context). It’s interesting that dietary fibre is considered as a carbohydrate-amount issue in the United States. To my mind it is very much a carbohydrate quality issue.
Mean adult intake of carbohydrate in Australia is about 46% of daily calories, right at the lower end of recommended intake range. This was perceived as low by some speakers and a reason for focussing on glycaemic index as the preferred means of lowering the total glycaemic load of the Australian diet. Others saw the current intake as ‘moderate’, pointing out that the beneficial diets in the Diogenes study contained just 43% of calories from carbohydrate – below the lower boundary of recommended carbohydrate intake.
I introduced my talk by arguing that both the upper and lower boundaries of carbohydrate intake were too high. They were framed at a time when it was thought that a higher percentage of dietary energy from fat was detrimental to health. However, the preferred model for healthy eating is now one with more unsaturated fats and less of both saturated fat and carbohydrate – a Mediterranean-type diet.
The long-held view that carbohydrate-rich foods are protective against heart disease, or at least benign, turns out to be wrong. Carbohydrate recommendations are too high but which carbohydrate-rich foods should be recommended in a healthy diet and which foods should be culled?
One of the most important findings from nutrition research in recent years was that carbohydrate confers similar risk for coronary heart disease to saturated fat. This turned 20 years of dietary advice on its head as it meant that the long-recommended low fat diet was not protective against heart disease. It followed that carbohydrate recommendations were too high and if lower intakes of carbohydrate were to be recommended, it would make sense to preference ‘good’ carbohydrate.
But what is good carbohydrate? Ask this question to a room full of nutritionists and the argument will go on for hours. Thirty years ago starch was considered good and sugars were bad, based on the assumption that starch was digested more slowly and raised blood glucose levels more gradually than sugars. However, studies of glycaemic index showed this assumption to be wrong. So should nutritionists forget about sugar and start recommending low GI foods? There are also arguments over whether ‘wholegrain’ or dietary fibre is the better measure of a good cereal food. In the United States, nutrition authorities have adopted nutrient density as an over-arching principle of their latest dietary guidelines. It would certainly make sense to favour nutrient-rich carbohydrate foods if total carbohydrate intake (or calories) was to be limited. So there are lots of options and opinions but no consensus on what represents good and bad carbohydrate.
Against this swirling background Professor Manny Noakes from CSIRO and I recently published a new model for assessing the nutritional quality of carbohydrate-rich foods.