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).
At last a trial of monounsaturated-rich Mediterranean diets for the primary prevention of cardiovascular disease has been published and the results are impressive. The missing piece of the puzzle is now in place. Mediterranean-type diets, moderate in total fat but enriched with unsaturated fats, are now the preferred model for healthy diets. But will nutritionists pay any attention or cling to the low fat dogma for a little longer?
Although advice to eat less saturated fat has been a fixture in Dietary Guidelines for three decades, the last four years have seen a spirited debate about what should take its place in healthy diets. As saturated fat is a macronutrient, one can’t just ‘eat less saturated fat’ and maintain energy balance. Saturated fat needs to be replaced by something else, such as carbohydrate or unsaturated fats. Carbohydrate is now considered a poor replacement for saturated fat as these two macronutrients confer the same risk for heart disease. This leaves mono- and polyunsaturated fats as the better options to replace saturated fat, but which of these should be preferred?
If your job was to sell products rich in saturated fat, current nutrition guidelines and policies would be a real impediment. So what would you do?
In the 1980s, human rights lawyer Geoffrey Robertson became a media personality hosting a television series dealing with ‘Hypotheticals’. He would outline a hypothetical situation and then invite prominent citizens to play imagined roles of the key players addressing various aspects of the situation, thereby exposing the various interests at play.
Let’s play ‘Hypotheticals’. I’ll be the moderator. You can play the role of the food company Chief Executive, Public Relations Guru or Ethicist.
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.
On the weekend a story by lawyer David Gillespie was published in several newspapers promoting his new book titled ‘Toxic Oil’. I’ve also tracked down an extract from his book on the internet. Mr Gillespie’s theme is that the consumption of vegetable oils, especially oils rich in omega 6, is killing us.There are so many errors and misleading statements in these short extracts that I can’t say I am looking forward to reading the full book. Here is a taste.
Gillespie says: … the amount of omega 6 oil we consume has exploded … our average polyunsaturated fat intake is currently … 11 per cent of our total calorie intake – more than double what it was in 1996.
This is just plain wrong. Intake of polyunsaturated fat in Australia has never been anywhere near as high as 11 percent of daily calories and rather than ‘exploding’ it has been declining for three decades.
The evidence on this issue is available to all in the two National Nutrition Surveys in 1983 and 1995, two CSIRO surveys and the 2007 Children’s Nutrition and Physical Activity Survey. The overall picture is one of a steady decline in polyunsaturated fat intake from 1983 until the present. Page 17 of the latest survey report shows children’s intake of polyunsaturated fats to be just 4 percent of total calorie intake across both genders and all age groups, about a third of that claimed by Mr Gillespie. Children’s intake of polyunsaturated fat is little different from the mean intake of men and women of 4.5 percent of daily calories observed in the last survey of adults in 1995.
Where did Mr Gillespie get his figures from?
The most notable shift in the latest Dietary Guidelines is the move away from the low fat diet. The emphasis is now on fat type. But how will healthy eating advice evolve from here?
The first Dietary Guidelines in Australia were released in 1980 and recommended restriction of the total amount of fat in the diet as a strategy for chronic disease prevention. In the following 20 years this piece of dietary advice took precedence over all others and dominated the nutrition landscape. However, the writing has been on the wall for the low fat diet for many years now.
The Five Food Groups concept has been a cornerstone of nutrition education for decades. But are they based on good science and logic? Do the Five Food Groups make sense?
Food groups and ‘distinguishing nutrients’
The concept of food groups has been central to nutrition education in many countries for decades. It’s a simple idea: different types of foods make distinctive contributions to the diet so eating a variety of foods from the different food groups should ensure adequate intakes of essential nutrients.
Although all whole foods contain small amounts of a wide variety of nutrients, the distinctive contribution of a food group is due to 4-6 ‘distinguishing nutrients’ found in abundance. As foods in the same food group share distinguishing nutrients they can be exchanged without compromising nutrient intake. This nutritional equivalence allows flexibility in food choice.
As concern about the health implications of the obesity epidemic has increased one frequently mentioned claim is that the current generation will be the first to live shorter lives than their parents. The assumption is that the effects of obesity on the risk for chronic disease are so significant that life expectancy will inevitably fall. But new evidence suggests that this assumption may be wrong.
A new meta-analysis of the effects of overweight and obesity on all-cause mortality was published this month in the Journal of the American Medical Association. The analysis included data from 97 studies from around the world, providing a combined sample size of more than 2.88 million subjects and more than 270,000 deaths.
The risk of death of all obese subjects (BMI>30) was substantially and significantly higher (18%) than that of subjects of normal weight (BMI 18.5-25) – the sort of finding that we have come to expect. However, the results told a different and perplexing story when narrower weight categories were considered. For example, those who were overweight (BMI 25-30) experienced 6 per cent lower risk of mortality than subjects of normal weight. Subjects with grade 1 obesity (BMI 30-35) had the same mortality risk as subjects of normal weight. Consequently, the mortality risk associated with obesity appeared to be due entirely to higher grades of obesity – BMI greater than 35, which was associated with a 29% increase in risk.
At last week’s Nutrition Society of Australia conference a debate was held on the topic “Fortified foods do more harm than good”. It was a fizzer with those supporting the proposition being unable to mount any serious arguments. A large majority of the audience disagreed with the idea both before and after the debate. But this was a very informed audience with deep knowledge of the rationale for fortification. Among less scientific groups hostility to food fortification appears to be growing. What’s the problem?
‘Tampering with the food supply’
One popular dietary myth is that the consumption of simple, minimally processed foods automatically translates into a healthy diet. As a consequence, any ‘tampering with the food supply’ by faceless scientific types is treated with suspicion and resisted. The defense of naturalism may be logical to a naive audience but it ignores the history of nutrient deficiency in humans. Even today in parts of Tibet a high percentage of the population, consuming a diet of simple, minimally processed foods, suffers from serious intellectual impairment due to iodine deficiency. One of the simplest dietary interventions of all – the addition of iodine to the salt used in food preparation – is all that it takes to solve this crippling problem.