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Part 2: dietary and lifestyle factors in the management of type 2 diabetes mellitus.

Abstract

The role of diet in managing type 2 diabetes is discussed. The impact of fibre, fats and protein are considered. Recommendations of appropriate dietary modifications are provided.

Reference

Boylan M. Part 2: Dietary and lifestyle factors in the management of type 2 diabetes mellitus. Journal of the Australian Traditional-Medicine Society 2007;13(1):15-17. (13 references).

Keywords: Type 2 diabetes mellitus; Diet; Fibre; Fats.

Introduction

The first article of this series looked at the alarming increase in type 2 diabetes, and why complementary medicine practitioners are well placed to significantly assist in the management of this condition (see Boylan M. Part 1: Dietary and lifestyle factors in the management of type 2 diabetes mellitus. Journal of the Australian Traditional-Medicine Society 2006;12(4):189-193).

The first management strategy considered was the use of the glycaemic index. The use of this index as a primary intervention was found to be questionable, and it was suggested that perhaps the glycaemic load was the more useful measurement. This second article looks at the broader dietary measures to help manage this modern day scourge.

But first it is useful to again stress why as complementary medicine practitioners we can make a real and significant contribution in the efforts to stop the increase in diabetic diagnoses and the resulting morbidity and even death.

It is known that without aggressive intervention such as dietary and lifestyle changes around half of pre-diabetic patients will develop type 2 diabetes within 10 years (1). Additionally, but unsurprisingly, the best results from non-pharmacologic interventions have been shown to occur when that intervention is provided on a continuing one-on-one basis by a health care practitioner (2). So as complementary medicine practitioners we are at the forefront in the fight against this epidemic.

Carbohydrates

In the first part of this series the quality of carbohydrates was discussed by examining the impact of the impact of the glycaemic index and glycaemic load of foods. It was concluded that the Diabetes Australia recommendation was appropriate in that diets be:
 of low energy density and containing a wide range of
 carbohydrate foods rich in dietary fibre and of low glycaemic
 index (cereals, vegetables, legumes and fruits) (4).


Controversy however still exists regarding what is the best carbohydrate to fat ratio of a diet designed to help manage diabetes, with a primary worry being whether or not high long term intakes of carbohydrates (or fats) may prove harmful. This concern results, at least in part, from the possibility that the repeated stimulation of high insulin production due to a high carbohydrate diet may hasten the onset of type 2 diabetes (3).

Therefore while these doubts exist it is recommended the Diabetes Australia recommendation be followed.

Why Rich In Fibre?

Studies have consistently found that fibre intake is inversely associated with the development of type 2 diabetes. This link is long established, having been demonstrated since the 1970s (3). In addition to being protective against the onset of type 2 diabetes, some studies have suggested that fibre improves insulin sensitivity. Consequently low dietary fibre may actually be a cause of type 2 diabetes (3).

Studies have shown that high carbohydrate diets, and thus high fibre diets, improve glycaemic control. Fibre supplementation has also been shown to lower post-feeding blood glucose levels and insulin levels, as well as improving long term glycaemic control (3). But what fibre is best, and how much is needed?

Well designed studies have shown conflicting results as to whether soluble fibre or insoluble fibre yields the best results. Also, the studies generally suggest that fibre intakes may need to be higher than the sometimes recommended 25 g/day. This lack of precision in both type and quantity of fibre means that 'it may be most appropriate to emphasise appropriate carbohydrate sources rather than specify quantities' (3).

The above conclusion is also consistent with the before-mentioned recommendation by Diabetes Australia, that is to include in the diet a wide range of carbohydrate foods rich in dietary fibre, such as cereals, vegetables, legumes and fruits (4). Specific foods which are primary sources of fibre include oat bran, wholegrain oats, wheat bran, celery, dried beans, psyllium seed husk, pectin and broccoli (5).

Fats

High fat diets may be detrimental to glycaemic control. High fat diets result in decreased binding of insulin to its receptors, impaired glucose transport, the accumulation of triglycerides and reduced concentrations of the enzyme glycogen synthase that catalyses the conversion of glucose to glycogen (3).

Importantly however, studies looking at effects of the amount of fat consumed in human diets have produced inconsistent results (3,6). Thus it is necessary to look at the type of fat as well as the overall quantity.

Saturated Fats

High saturated fat diets are associated with increased fasting glucose levels and increased insulin levels. High saturated fat diets are also linked to reduced insulin sensitivity as well as an increased likelihood of developing type 2 diabetes (3).

Prediabetic and diabetic patients should be encouraged to replace saturated fats with high fibre carbohydrate foods and/or with unsaturated fat food sources (1). Saturated fats should not provide anymore than 10% of energy requirements (4).

Unsaturated Fats

Mono and polyunsaturated fats on the other hand have been associated with a lower risk of developing type 2 diabetes. These fats have been shown to reduce fasting glucose levels and improve insulin sensitivity (3). But again, the picture concerning unsaturated fats is not clear-cut.

Some studies have shown that high amounts of mono-unsaturated fats in a diet may contribute to an increase in the risk of developing type 2 diabetes. This becomes additionally complex by the suggestion that this risk increase might be because mono-unsaturated fats in the typical Western diet are substantially obtained from sources, such as meat and dairy products, also high in saturated fats, and it is the effects of those co-existing saturated fats that are the problem (3).

The amount of unsaturated fat in a diet should also not be excessive. This was illustrated by a study showing that where mono-unsaturated fats were substituted for saturated fats in the diets of healthy subjects, the favourable effect of this substitution was negated once individuals obtained more than 37% of their daily energy requirements from fat (3).

Omega 3 Fatty Acids

Though there have been some studies suggesting a protective role of omega 3 fatty acids in the development of type 2 diabetes (6), these studies have been few and most intervention studies looking at the effects of omega 3 fatty acids have produced negative results (3). It remains debatable if the protective effect suggested in some studies looking at fish was due to the omega 3 fatty acids in the diet or the fish protein (6).

Trans-Fatty Acids

There are only limited studies as to the effects of trans fatty acids on glucose metabolism (3). However it is generally accepted that the effects of trans fatty acids are similar to those of saturated fats in raising plasma low density lipoproteins and lowering high density lipoprotein cholesterol. Thus it is suggested that in the management of type 2 diabetes the consumption of trans fatty acids should also be limited (7).

Fats in Summary

Accordingly, a diet where most fat is unsaturated and obtained primarily from plant and whole fish sources may be beneficial in preventing type 2 diabetes (6). Further, fats in total should not provide more than about one-third of total energy requirements, and saturated fats should provide less than 10% of the energy needs (4).

Protein

Although some small studies have shown that a high protein/ low carbohydrate diets may result in a reduction of serum glucose (8,9), there exists a number of studies which have shown that ingested protein does not contribute to postfeeding serum glucose levels (7,10). Additionally the peak glucose response to a carbohydrate alone meal is similar to that of a protein and carbohydrate meal, suggesting that protein does not slow the absorption of carbohydrates (7). Therefore any benefit of high protein/low carbohydrate diets might arise from the reduced carbohydrate contents of those diets.

That is not say that protein has no role to play in the management of type 2 diabetes. Protein does stimulate the secretion of insulin in those individuals still capable of producing insulin (10). Further it has been shown that in type 2 diabetic patients moderate hyperglycaemia results in increased protein turnover (7).

Protein and Nephropathy

When considering protein and the diabetic patient it should be kept in mind that diabetic nephropathy is a significant cause of morbidity and mortality, and is now one of the most common causes of end-stage renal failure. So as to not aggravate this condition, the avoidance of high protein intake in diabetic patients at risk of developing diabetic nephropathy must be taken into consideration (11).

Vegetarian Diet

As at 2003 there had been no major studies which examined the benefits of a vegetarian diet without also including weight loss. Nevertheless there are many aspects and nutrients of a vegetarian based diet that might assist in the control of serum glucose and blood lipid levels. Additionally if plant based proteins were preferred to animal based proteins, there may in the long term be a reduction in the risk of type 2 diabetic patient developing renal disease (12).

Therefore, and although relevant studies need to be undertaken, vegetarian diets may result in metabolic advantages for preventing and treating type 2 diabetes (12).

Conclusion

Wein concluded in part:
 Incorporating the most effective proportions of
 macronutrients into dietary treatment plans will positively
 influence the overall health and quality of life of
 persons with prediabetes. As science emerges, nutrition
 professionals must continuously explore and embrace
 novel strategies to assist persons with prediabetes adopt
 and sustain healthy dietary lifestyles that target glycemic
 and lipid goals (1).


To achieve effective proportioning of macronutrients, it is suggested:

* That diets be of low energy density and contain a wide range of carbohydrate foods rich in dietary fibre.

* As a minimum, the Australian Government recommended fibre intakes of 30 g/day for men and 25 g-30 g/day for women are met (13).

* The above two recommendations will supply foods which generally will also have a low glycaemic index. However the glycaemic load of a meal may be the more significant measure than the glycaemic index.

* Limit energy from fats to around 30%.

* Reduce as much as possible the consumption of saturated fats. Aim to have no more than 10% of energy provided from saturated fats.

* Source unsaturated fats primarily from plant sources and whole fish.

* Maintain adequate protein, but be alert to potential concerns in those patients at risk of developing diabetic nephropathy.

The above recommendations have included the preference for diets to be of low energy density. This specific recommendation is a brief insight to one of the two major topics to be considered in the third and final Part of this series. Those two major topics are weight (fat) loss/management and exercise. As will be demonstrated in the concluding Part of this series, these two interventions are of primary and vital importance in the non-pharmacological management of type 2 diabetes.

References

(1) Wien M. A review of macronutrient considerations for persons with prediabetes. Topics in Clinical Nutrition 2006;21(2):64-75.

(2) Lindstrom J, Louheranta A, Mannelin M, Rastas M, Salminen V, Riksson J, Uusitupa M, Tuomilehito J. The Finnish diabetes prevention study (DPS). Diabetes Care 2003:26(12):3230-3236.

(3) Steyn N, Mann J, Bennett P, Temple N, Zimmet P, Tuomilehto J, Lindstrom J, Louheranta A. Diet, nutrition and the prevention of type 2 diabetes. Public Health Nutrition 2004;7(1A):147-165.

(4) O'Dea K (Chairperson). Part 2--Evidence based guideline for the primary prevention of type 2 diabetes. Sydney: Diabetes Australia. http://www.diabetesaustralia.com.au/_lib/doc_pdf/NEBG/PP/ Part2--Prevention--311201.pdf. Accessed 8 February 2007.

(5) Braun L, Cohen M. Herbs & natural supplements An evidencebased guid.e 2nd ed. Sydney:Churchill Livingstone, 2007.

(6) Parillo M, Riccardi G. Diet composition and the risk of type 2 diabetes: epidemiological and clinical evidence. British Journal of Nutrition 2004;92:7-19.

(7) Franz M, Bantle J, Beebe C, Brunzell J, Chiasson J, Garg A, Holzmeister L, Hoogwerf B, Mayer-Davis E, Mooradian A, Purnell J, Wheeler M. Nutrition principles and recommendations in diabetes. Diabetes Care January 2004;27(S1):S36-S46.

(8) Nuttall F, Gannon M, Saeed A, Jordan K, Hoover H. The metabolic response of subjects with type 2 diabetes to a high-protein, weight-maintenance diet. Journal of Clinical Endocrinology & Metabolism 2003;88(8):3577-3583.

(9) Gannon M, Nuttall F. Effect of a high-protein, low-carbohydrate diet on blood glucose control in people with type 2 diabetes. Diabetes 2004;53(9):2376-2382.

(10) Choudhary P. Review of dietary recommendations for diabetes mellitus. Diabetics Research And Clinical Practice 2004;65(S):S9-S15.

(11) Haslett C, Chilvers E, Hunter J, Boon N (editors). Davidson's Principles and Practice of Medicine. 18th ed. Edinburgh: Churchill Livingstone, 1999.

(12) Jenkins D, Kendall C, Marchie A, Jenkins A, Augustin L, Ludwig D, Barnard N, Anderson J. Type 2 diabetes and the vegetarian diet. American Journal of Clinical Nutrition 2003;78(suppl.):610S-616S.

(13) Australian Government, Department of Health and Ageing, National Health and Medical Research Council. Nutrient Reference Values for Australia and New Zealand. 2006. http://www.nhmrc.gov.au/publications/_files/n35.pdf. Accessed 11 February 2006.

Matthew Boylan operates a herbal medicine practice in Leichhardt, Sydney. He regularly writes articles on health research for this Journal. Telephone (02) 9560 8450.
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Author:Boylan, Matthew
Publication:Journal of the Australian Traditional-Medicine Society
Geographic Code:8AUST
Date:Mar 1, 2007
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