NHMRC Public Consultations

Skip Navigation and go to Content
Visit NHMRC website

Australian Dietary Guidelines submission

ID: 
23
Personal Details
First Name: 
Jennifer
Last Name: 
Elliott
Online comments
Specific comments: 
General comments
Comments: 

Thank you for the opportunity to comment on the latest version of the dietary guidelines.

 

I would like to start with a general comment. Inherent in the guidelines is the assumption or belief that there is one way of eating that will suit everyone.  I believe this to be a mistake and appreciate the opportunity to explain why.

 

As an example, I’d like to look at the recommended number of serves of grains. The guidelines suggest that all Australian adults should aim for 6 serves of grains per day. It is stated that evidence for the association of grain foods with reduced risk of CVD, type 2 diabetes and excess weight has strengthened since the previous guidelines, however I note that such associations are still classed as ‘probable’.

 

The problem that I see with this example in particular, and with others in the guidelines, is that often the recommendations are drawn from population studies rather than from an understanding of metabolic or disease processes.

 

Many of the recommendations in the dietary guidelines derive from population studies such as the Nurses Health Study. These studies show statistical relationships only and because they tell us nothing about cause and effect, they should not be used to inform diet advice. Such studies can alert us to possible links between diet and disease but these links need to be investigated further before nutrition advice is given.

 

How information about diet is collected and 
secondly how it is interpreted is important to know. In the Harvard studies a questionnaire
 asks for an estimation of how much and 
how often in the past year participants ate each of approximately
100 different foods. There are obvious short-comings to this method of data 
collection. For example, how accurately can a person determine how often they 
ate butter in the last year? Most people do not quiz food-
outlets and friends when eating out as to the ingredients in 
the meal. Many can change their regular eating pattern when on holidays, to lose weight or when sick. Some can’t remember what they ate yesterday let alone last month.

Inaccuracy in food data collection is, however, a small 
consideration in comparison to how such data is interpreted 
in these studies. Firstly, the participants are followed for many years and the researchers are
 informed of what illness/disorders develop, as well as
 causes of death. Health and dietary information are entered
 into a database. Vast amounts of data are then available for
 statistical analysis and relationships between any two 
variables can be made. All that needs to be done is to 
select a food item and a disease, and the computer 
calculates the statistical relationship between them. Millions of possibilities exist depending on the questions
 asked: legume intake and gallstones; jam and arthritis; saturated fat and warts; milk and depression; cereal intake and diabetes.

These associations are reported as positive or negative—
intake of the food is statistically associated with a
 greater or lesser incidence of the disease. Such 
associations have nothing to do with cause and 
effect.

 

If a lower incidence of diabetes is reported in those 
that eat more grains, this does not mean that eating grains protects against developing diabetes as is often reported. This estimation is purely hypothetical; arrived at by the use of statistical modeling and 
incorporates a flawed assumption of causation.

 

Much of the diet advice given today eg to eat a minimum of two fruits per day, 6 serves cereal etc uses this type of modeling and hasn’t been tested to see if there are any unforeseen adverse effects in some people.

 

I believe that the dietary guidelines have shaped our thinking about diet over the last 30 years in unforeseen negative ways. With the focus on reducing fat intake for so many years, by default carbohydrate became the healthy alternative. And carbohydrate foods such as grains and fruit continue to be recommended.

 

This has created a problem for a number of people who metabolise carbohydrate in a particular way and I believe has put these individuals at risk of developing obesity, type 2 diabetes and CHD.

 

I know this is getting a bit long but I’d like to explain this in some detail to underline my point that the current diet advice does not suit everyone.

 

Carbohydrate foods such as bread, potato, rice, pasta, cereals, fruit, milk, sugar etc are broken down to simple sugars, predominantly glucose. Glucose is absorbed into the blood and the subsequent rise in BGL triggers the pancreas to release insulin. Insulin aids in the transport of glucose into cells where it is either stored as glycogen or used to provide energy.

 

Many people are able to metabolise carbohydrate foods in this way. They are likely to release the right amount of insulin in response to a rise in BGL, glucose is quickly cleared from the blood into cells, BGLs remain in the ideal range, our person has lots of energy and doesn’t gain weight easily. The recommended servings of carbohydrate foods in the guidelines may suit this person.

 

However insulin resistant people have a different metabolic response after eating carbohydrates. If their muscles are resistant to the action of insulin, glucose does not enter muscles quickly and an enhanced insulin response may be precipitated in an attempt by the body to maintain glycaemic control

 

High insulin levels may maintain ideal glucose levels for many years before type 2 diabetes develops, however there is a price to pay for this.

 

In the scientific literature, there is documentation that high insulin levels are associated with high triglycerides, low HDL, fatty liver, sleep apnea, excessive hunger, weight gain, central adiposity, difficulty losing weight, tiredness, reflux/ indigestion, type 2 diabetes, gout, hypertension, anxiety, depression, loss of muscle mass, microalbuminuria, inflammation, CHD, poorer breast cancer prognosis and memory impairment. (I can provide references for all these associations if you’re interested)

 

 

 

As a dietitian, I routinely see a combination of these features in my clinical practice. Some features may be present in younger people eg excessive hunger, craving carbs, mood swings, central adiposity, mouth breathing. Older people often have many more features.

 

There is an abundance of evidence in the literature that a lower carbohydrate diet is beneficial in the management of insulin resistance. That is outside the guidelines but I’d like to make the point that by recommending a diet with a liberal intake of carbohydrate for all Australians, the guidelines are not considering the metabolic effect of this intake on those that have a genetic predisposition to insulin resistance.

 

It’s possible that the lower fat / liberal carbohydrate diet as the diet of choice for everyone, which has been with us for approx. 30 years, has contributed to the increased prevalence of obesity and type 2 diabetes that we are experiencing.

 

Our dietary guidelines are based on estimates of foods required to achieve adequate nutrient intake, data from population studies etc, however the vital link ie the understanding that people can differ in their metabolic response to food, I believe is missing.

 

For those people who have an increased insulin response to carbohydrate foods, the recommended intake for carbohydrate foods may be too high. The resulting high insulin levels can put such individuals into ‘storage mode’, where there is an increased conversion of glucose to triglyceride in the liver, stimulation of visceral fat receptors to take up this fat (resulting in central obesity), impaired lipolysis and effects on hunger and satiety via alterations to cortisol and serotonin levels.

 

High insulin responses to carbohydrate foods can occur at any age. From a personal perspective, my daughter was diagnosed with insulin resistance at 14 years old and it explained why she had a weight problem, mood swings and low energy. She has controlled this condition with a lower carbohydrate diet for many years, without the need for medications. An increase in her carbohydrate intake results in very quick changes to her mood, hunger and energy. Her mood may drop suddenly and she feels like crying; she can be hit with a sudden lethargy and need to sleep; and once she starts eating carbohydrate she craves more.

 

 All these reactions can be explained by changes in her biochemistry. These have been documented in the literature to occur when insulin levels are increased. If she ate the recommended amounts of carbohydrate foods in the guidelines she would be in a constant state of mood swings, excessive hunger and cravings, low energy and poor concentration. With the known effect of high insulin in promoting central adiposity, she would also likely be overweight or obese.

 

And she is not alone in the way she metabolises carbohydrates. The SPANS study published in 2004 estimated that approx. 20% of 15-16 years had high insulin levels. In addition 25% of the population is estimated to fit the criteria of metabolic syndrome, of which insulin resistance is a crucial component.

 

When my daughter was diagnosed with insulin resistance I read over 1500 articles trying to understand the condition. The evidence points to it resulting from the way some people metabolise carbohydrate and this in turn is influenced by genetics, diet and exercise.

 

The capacity to convert glucose to triglyceride for storage as fat gave our ancestors an advantage in times of food shortage and this ability remains with many of us to varying degrees. Some people do not make this conversion easily but others, like my daughter even at a young child, are very adept storers.

 

By not taking this difference into account, following the guidelines pertaining to carbohydrate intake (including fruit as well as grains) may result in this underlying tendency expressing itself.

 

It is possible that rise in obesity and type 2 diabetes can be the result of successfully influencing a population to believe that fat is fattening and that carbohydrates are good. 

 

And this is where we have another problem with dietary guidelines ie where specific amounts of foods are recommended.

 

 It is not possible to advise anyone, including an insulin resistant person, on how much carbohydrate they can consume without triggering an excessive insulin response. This is because of the interplay between exercise (which improves insulin sensitivity), diet and individual sensitivity (probably largely determined by genetics).

 

Unfortunately I haven’t finished yet.

 

My next point is along similar lines ie my opinion that there is not one set of guidelines to suit everyone, and it concerns the recommendation to restrict salt intake.

 

Recent studies have reported an association between low salt intake and adverse outcomes.

 

Some studies have reported that a low sodium intake can contribute to hypertension.

 

Eagan B.M. et al (1994) Renin and aldosterone are higher and the hyperinsulinemic effect of salt restriction greater in subjects with risk factors clustering.

Am J Hypertension, 7, 886-893

 

 

And there is evidence that salt restriction can make insulin resistance worse.

 

Ames R.P. (2001) The effect of sodium supplementation on glucose tolerance and insulin concentrations in patients with hypertension and diabetes mellitus.

Am J Hypertension, 14, 653-659

 

Feldman R.D. et al (1996) Dietary salt restriction increases vascular insulin resistance, Clinical Pharmacology & Therapeutics, 4, 444-451

 

Historically a recommendation was made concerning salt intake without taking into account potential adverse effects on some people and people who are insulin resistant appear to be more susceptible to adverse effects of salt restriction.

 

At present, when I.R./ hyperinsuinaemia is estimated to affect approx. 4 to 5 million Australians, many people’s health could potentially be adversely affected by continuing the low-salt message without qualification.

 

That’s it!

 

Thank you for your time.

 

 

 

 

 

 

 

Page reviewed: 3 January, 2013