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Nutritional management of blood lipids in diabetes

Paul McArdle

Registered Dietitian and Spokesperson for the British Dietetic Association

This article looks at dietary advice to improve blood lipid profiles and reduce cardiovascular risk in diabetes, which includes the promotion of 'cardio-protective' foods that won't necessarily lower blood cholesterol

People with diabetes report that the dietary element of managing their condition has a significant negative impact on quality of life. They also tell us that we (healthcare professionals) contradict one another when giving dietary advice. However, dietary interventions in diabetes have been shown to significantly improve both glycaemic control and cardiovascular disease (CVD) risk factors, particularly in type 2 diabetes.1 It is, therefore, vital that all healthcare professionals working in diabetes are able to identify the correct evidence-based dietary messages and that they have the skills in behaviour change to support their patients.

Those with diabetes have a three- to four-fold increased risk of CVD compared to those without and, as such, it is appropriate to target dietary management in a similar way to those with existing CVD. Dyslipidaemia is, of course, one of several risk factors for CVD so it is important to consider the other modifiable risk factors, such as blood pressure, smoking, weight and physical activity. Weight loss and physical activity have both been shown to play an important role in controlling blood pressure and improving lipid profiles, and consequently CVD outcomes.2,3 Even a modest weight loss of 5-10% can lead to clinically significant changes.

A reduction in saturated fats (also known as saturated fatty acids or SFAs) should be a priority. Saturated fats are derived mainly from animal sources, such as cream, butter, cheese and meat, and they currently represent 12.8% of our total food energy in the UK.4 Figure 1 shows the main sources of saturated fats in our diet, according to the National Food and Nutrition Survey carried out in 2009.

[[Fig 1 lipids]]

Why target SFAs?
Saturated fats are most closely associated with atherosclerosis and have the greatest impact on blood cholesterol levels. International nutritional guidelines for diabetes unanimously recommend a reduction in SFAs, and target levels range from less than 7% to less than 10% of food energy.5-7 But practically speaking, what does this mean? Some studies have suggested it is difficult to achieve 7% of food energy from SFAs and that aiming for 10% is still beneficial, provided the overall composition of the diet is considered to be 'heart-healthy'. In reality, we should support our patients to achieve the lowest level of saturated fat that is practical for them.

The National Diet and Nutrition data show us that dairy foods make the single largest contribution to our SFA intake, which mainly refers to whole milk and cheese. Sausages are one of the main sources of SFA in the meat category, and biscuits the main source within the cereals group. So general advice to reduce saturated fats could be targeted towards lower fat milk and cheese (or simply less cheese for some people); less processed meat such as sausages; and fewer biscuits, cakes and pastries.

Advice to individuals should be tailored to their own saturated fat intake. For example, if a patient regularly eats toast and sandwiches the contribution of their fat spread will be more significant and hence a change here will have a greater impact. But what should the saturated fat be replaced with? The simple answer is unsaturated fatty acids; but more specifically monounsaturated fatty acids (MUFA). In reality, all fats are combinations of the three main types of fatty acid but will usually predominate in one fatty acid. Table 1 outlines some examples of foods that are sources of each of the three fatty acids - SFAs, MUFAs and polyunsaturated fatty acids (PUFAs).

[[Tab 1 lipids]]

Olive oil is often promoted as a healthier alternative to other types of oil. However, it is still 99.9% fat and about 100 calories per tablespoon, the same as all other oils. Although changing to a monounsaturated fat, such as olive oil, will have a beneficial impact on lipid profiles, patients could very easily gain weight if the quantities aren't controlled. It's also worth noting that pure vegetable oil (usually made with rapeseed oil in the UK) has a similar fatty acid composition to olive oil and is a much cheaper alternative.

Evidence suggests that MUFAs can have a positive impact on the lipid profile by reducing harmful low-density lipoprotein cholesterol (LDL-C) while causing a modest rise in the protective high-density lipoprotein cholesterol (HDL-C).8,9 Saturated fats on the other hand cause an increase in both LDL-C and HDL-C.

Trans-fatty acids ('trans fats' or TFAs) are unsaturated fats produced through an industrial process and are used by food manufacturers in cakes, biscuits and pastries, for example. They have been found to be at least as harmful as saturated fats and some authorities, for example in New York City, have even banned their use in restaurants and takeaways. In the UK we are already consuming below the recommend percentage of food energy from these fats; however, it is possible that consumption is skewed towards certain pockets of society and people who consume more processed foods.

Mediterranean diet
A Mediterranean diet can be described as one that is low in saturated fat, but rich in fruits, vegetables, legumes, wholegrain cereals, fish and low-fat dairy foods. The diet, in addition to regular physical activity, emphasises "abundant plant foods, fresh fruit as the typical daily dessert, olive oil as the principal source of fat, dairy products (principally cheese and yogurt), and fish and poultry consumed in low to moderate amounts, zero to four eggs consumed weekly, red meat consumed in low amounts, and wine consumed in low to moderate amounts". Total fat in this diet is 25-35% of calories, with saturated fat at 8% or less of calories.10

There is a low consumption of meat and meat products, and monounsaturated fats are the main source of dietary fats. Studies that have incorporated a reduced-sodium Mediterranean diet have resulted in improvements in HDL cholesterol, triglyceride levels and blood pressure.11-13 These improvements are thought to result from the overall composition of the diet, and the constituent components taken individually do not produce the same outcomes.14 The Mediterranean diet also highlights the importance of the type of fat over the quantity since it is not necessarily low in fat but it is low in saturated fats.

Oily fish
Omega-3 is a type of polyunsaturated fatty acid (PUFA) that is found in oily fish. There is good evidence that increasing intake of omega-3 following myocardial infarction reduces mortality; but the evidence for primary prevention in intervention studies is less clear. However, we know that populations that consume more oily fish do experience lower levels of CVD.15-17 People with diabetes are advised to consume at least two portions of oily fish per week (see Box 1 for examples of oily fish).

[[Box 1 lipids]]

It has been shown that high intakes of dietary fibre (especially soluble fibre) can have beneficial effects on blood lipid profiles in people with diabetes. Soluble fibre is found in fruit (including apples and oranges) oats, legumes and some vegetables, such as peas, carrots and broccoli. Reductions of up to 2-3% in total cholesterol and up to 7% for LDL cholesterol have been demonstrated from high intakes of soluble fibre.18 In the UK, oat-containing products are permitted to carry a health claim for soluble fibre, provided they contain one quarter of the 3 g per day needed to see an effect - although intakes of 10 g or more per day of soluble fibre are suggested in diabetes.

Plant stanols and sterols
Plant stanol and sterol esters are the active ingredients found in products such as Benecol and Flora Pro.Activ. They work by reducing the amount of cholesterol the body absorbs from food and the quantity reabsorbed from bile, and they have been proven to reduce total and LDL cholesterol by about 10%.19 This effect is also seen in people already taking cholesterol-lowering statin drugs.20 These functional foods can be recommended to people with diabetes but affordability may be a consideration and the effects last only as long as the products are being consumed, so they need to be continued indefinitely. There is a dose-responsive effect up to an optimal dose of about 2 g per day so patients should be advised to follow the manufacturer's recommendations.

Nutritional supplementation
There is little evidence for nutritional supplementation in the prevention of CVD. However, in patients with elevated levels of blood triglycerides studies have shown that supplementation with up to 3 g per day of omega-3 (DHA and EPA) can improve triglyceride levels without adverse effects on other lipids or glucose control.21

There are clearly many dietary changes that, taken together, could have a significant clinical impact on lipid profiles and cardiovascular risk (see Box 2). However, not all patients will be able or willing to make every change that has been suggested in this article.

[[Box 2 lipids]]

Patients themselves are best placed to make decisions about which changes are most appropriate for them, once they are furnished with evidence-based facts on the subject. The use of excellent communication skills to help patients set realistic
goals and develop successful action plans cannot
be underestimated.

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Diabetes UK

British Dietetic Association
The BDA produces a range of food fact sheets available to download from the website

British Heart Foundation

Your comments (terms and conditions apply):

"Asda have started to sell a cholesterol lowering yogurt - four small drinks in each pack for £1-28p. Each drink contains 2gr of plant stanols, I think this is a really good and inexpensive way of ensuring the correct amount of stanols for optimum effect. I am now recommending this drink to all my patients who are presenting with raised lipids who are happy to try dietary modification along with encouraging oily fish and fibre and reducing sat. fat intake. time will tell if it works" - Mari, Lancs