Title: The role of carbohydrates in the care of people with type II diabetes who are obese

Key words: obesity, cardiovascular disease, CVD, type II diabetes, diabetics, visceral adiposity, metabolic syndrome, exercise, diet, weight loss, weight reduction, low calorie diet, insulin, secretion, hyperglycaemia, hypoglycaemia, dyslipidaemia, adiposity, high carbohydrate diets, saturated fat, trans-fatty acid, fat, carbohydrate, glycaemic, intake, energy density, triglyceride, index, cholesterol, LDL, low density lipoprotein, fibre, fiber, soluble fibre, pulses, weight, public health, interventions

Date: Sept 2006

Category: Macronutrients, Specific conditions

Nutrimed Module:

Type: Article

Author: Morgan, G

 

The role of carbohydrates in the care of people with type II diabetes who are obese

 

Obesity, and its association with cardiovascular disease, poses the single greatest public health problem in the developed world. A recent National Health and Nutrition Health Survey in the US (Nelson 2002) has shown 82% of type 2 diabetics to be either overweight or obese. Prospective surveys have shown obesity promotes type 2 diabetes (Must 1999), the risk increasing by some 27% in those putting on at least 5 Kg of weight over any 10 year period (Ford 1997). Visceral adiposity and its association with the metabolic syndrome are closely linked to the pathophysiology of both cardiovascular disease and diabetes (Despres 2001). Inadequate exercise (69%), and poor diet (some two thirds of cases), were contributing factors in the NHANES survey (Nelson 2002).

 

Weight reduction remains central to diabetic management. Low calorie diets, regardless of their carbohydrate, saturated or unsaturated fat levels, have led to reductions in hyperglycaemia, insulin secretion and dyslipidaemia (Heilbronn 1999, Foster 2003). Fat intakes above 40% of total energy consumption, especially of saturated and trans-fatty acids, have been linked to adiposity and type 2 diabetes (Riccardi 2000), but similar associations have been made with high carbohydrate diets (Garg 1994, Parillo 1996). Fat and carbohydrate consumption are inversely correlated (Lissner 1995) so avoidance of either of these dietary extremes is essential in diabetic management. Due to its energy density and deleterious effect on glycaemic, lipid, and cardiovascular profiles, fat intake has been increasingly restricted in diabetic protocols over the last 50 years with a corresponding increase in carbohydrate consumption (Mann 2002).

 

The evidence on high carbohydrate diets is somewhat equivocal. Some studies have shown a beneficial effect of high carbohydrate diets on type 2 diabetes (Nuttall 1993, Hodge 2004). The majority do not, the consistent finding being an elevation of serum triglyceride levels (Mensink 1987, Garg 1994, Parillo 1996, Komiyama 2002). Most studies also show an aggravation of glycaemic control (Garg 1994, Parillo 1996, Riccardi 2000), though some studies show no effect or a beneficial effect (Komiyama 2002, Yang 2003). Such variability in research findings may reflect differences in study design and food composition. Carbohydrates with a low glycaemic index are characterized by a high fibre content (Jenkins 2002). Both have independently been shown to improve glycaemic control and reduced cholesterol, low density lipoprotein and triglyceride levels (Giacco 2000, Chandalia 2000, Brand-Miller 2003). A recent 8 year prospective trial (Schulze 2004) has shown both to be inversely correlated with the development of type 2 diabetes.

 

Soluble fibre, in particular, e.g. in foods such as pulses, has been linked to an improved metabolic profile, tighter weight control, and an improvement in the cardiovascular parameters associated with diabetes (Rizkalla 2002). Differences in research findings may therefore reflect food composition differences, as the deleterious effects of high carbohydrate diets have been shown to be negated by increasing their low glycaemic index and high fibre components (Riccardi 2000). 

 

The benefits of a high carbohydrate/ high fibre/low glycaemic index diet are twofold. Firstly, the lower fat content and the higher content of relatively satiating foodstuff is associated with a tightening of weight control. Secondly, the increased fibre and low glycaemic component is associated with a reduction in the abnormal glycaemic and lipid profile associated with the complications of type 2 diabetes, notably cardiovascular.

 

Although a meta-analysis of 14 studies (Brand-Miller 2003) recorded that the mean reduction of HbA1c levels between high and low glycaemic index diets was only 7.4% and the changes in fasting plasma glucose, total cholesterol, triglycerides and very low density lipoproteins were of a similar order between high and low fibre diets (Chandalia 2000), when taken together with diet-associated weight loss, the beneficial effects on diabetes have been shown to be substantial.

 

As little as a 5% loss of weight has been shown to produce significant improvements in glycaemic control (Parillo 2004). The same study claimed that, if improvements to the carbohydrate and fat components of the diet were combined with weight loss, an exercise programme and moderate alcohol consumption, the risk of developing type 2 diabetes would be reduced by some 87%. Anderson, in a meta-analysis of the available information (Anderson 2004), has recommended a carbohydrate intake of at least 55% of daily energy needs, with a favourable glycaemic index profile and inclusive of 25-50 G/day of dietary fibre. Fat intake should be maintained at less than 40% in order to modulate weight gain (Riccardi 2000). That these protocols are not being pursued diligently enough is testified to by the fact that, in the US, more emphasis has recently been placed on medical interventions to the detriment of dietary and lifestyle strategies, with an associated increase in the incidence and cardiovascular complications of diabetes (Koro 2004). This emphasizes the prime importance of public health measures in helping to control this disease.

 

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