NHD-EXTRA: CONDITIONS & DISORDERS
TYPE 2 DIABETES: LOW CARBOHYDRATE DIETS AS TREATMENT Alice Fletcher RD Community Dietitian, Countess of Chester NHS Foundation Trust
Alice has been a Registered Dietitian for almost three years working within NHS community-based teams. She is passionate about evidence-based nutrition and dispelling diet myths. Alice blogs about food and nutrition in her spare time. NutritionIn Wonderland.com
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There is increasing media coverage regarding low carbohydrate diets as a treatment for Type 2 diabetes (T2DM), particularly in place of drug therapies. As a result, more and more people with T2DM are asking if they should “cut out the carbs”. Many dietitians are finding that this style of eating is becoming more difficult to advise against. Is it time that we changed our practice? As a Community Dietitian who delivers diabetes education sessions to those diagnosed with T2DM, I am often asked if service users should “cut out the carbs”. Considering blood sugar levels are directly affected by the carbohydrates (CHOs) that we eat, this does seem like a logical solution and can at times be difficult to advise against. The television coverage of low CHO diets as a treatment for T2DM appears to be increasing over recent years. During an episode of Doctor in the House aired by the BBC in 2015, key sources of CHOs for the person with diabetes were removed, with emphasis placed on removing dairy and wheat containing foods. Time-restricted eating/fasting was recommended, along with suggesting that the 5-a-Day for the individual came from vegetables only, avoiding fruit completely. Shortly after this programme was aired, Dr Duane Mellor gave the following statement on behalf of the British Dietetic Association (BDA): ‘This advice is potentially dangerous with possible adverse side effects. Not only is there limited evidence around CHO elimination and time-restricted eating for those with diabetes, but cutting out food groups and fasting could lead to nutrition problems, including nutrient deficiencies and adversely affect their blood sugar control, particularly in individuals taking certain medications or insulin. ‘Whilst reducing refined CHOs and sugar intake is definitely a positive,
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many of the other recommendations lack evidence from scientific research base. People living with diabetes watching the programme are advised to stick with their current treatment and discuss any changes with their diabetes team, which can include a consultant or GP, dietitian and Diabetes Nurse.’1 The statement was clear: the advice given to hundreds of thousands of people in this programme was not supported by the BDA. The recommendation of low CHO diets for T2DM continues within magazines, newspapers and social media. Often there is emphasis on not needing to count calories and being able to eat as much fat as you would like to, as well as having increased satiety secondary to this. This mantra is particularly backed by Dr Mark Hyman, the American Author of Eat Fat, Get Thin. Dr Hyman is an advocate of a very low CHO diet for T2DM with the majority of calories coming from fat, followed by protein. Dr Hyman is also a fan of ‘bulletproof coffee’ (blending butter into black coffee). Within his latest book he argues that recommendations to cut down on fat and to base meals around starchy CHOs have fuelled the epidemic of obesity and T2DM.2 We know from national databases that across the UK, America and other countries, our intake of starchy CHOs has increased alongside intake of total fat and added sugars. Here in the UK, Dr Michael Moseley has written a book The Blood Sugar Diet
where a low CHO Mediterranean style diet is recommended. The advice within this is similar to that of Dr Hyman, with less sensationalism and dietary restrictions. CHOs such as quinoa, bulgur, whole rye, wholegrain barley, wild rice and buckwheat are recommended in sensible amounts.3 Dr Michael Mosley has T2DM and controls his blood sugar levels into the ‘normal’ range following this style of eating alongside intermittent fasting (the 5:2 diet). When it comes to Registered Dietitians, Dr Trudi Deakin is also an advocate of low CHO diets for the management of T2DM alongside ditching low fat products. Dr Deakin developed the X-PERT education programme for those with T2DM, and it is utilised by many NHS Trusts across the UK. In November 2015, Dr Deakin released a book Eat Fat, Step-by-Step Guide to Low Carb Living alongside the X-PERT programme. She highlights that the programme continues the same, but with less emphasis on low fat, and supports participants with trying different dietary approaches.4 If current trends persist, one in three people will be obese by 2034 and one in 10 will develop T2DM.5 Is it time that we changed our practice? WHAT IS CURRENTLY RECOMMENDED FOR THE DIETARY MANAGEMENT OF T2DM?
Low added (free) sugar diets are recommended for Type 1, 2 and gestational diabetes, as well as generally for a healthy balanced diet. Presently, adults are recommended to consume no more than 30g of added ‘free’ sugars per day (roughly seven sugar cubes), but they are estimated to consume on average two to three times this amount.6 When it comes to T2DM, the advice does
not differ, but added sugars are recommended to be reduced as much as possible.7 When it comes to starchy CHOs, we are recommended to have a large proportion of our diet based on them, as shown in the Eatwell Guide. The advice from Diabetes UK is actually quite vague, stating on their website: ‘Try to include some starchy foods every day.’ The reference intake for CHOs at present as listed on the NHS website, is 260g per day in total. It remains unclear exactly where this reference intake has been devised from. HOW CAN A ‘LOW CHO DIET’ BE DEFINED?
There is presently no specific definition of a low CHO diet, however, studies into low CHO diets usually use a maximum of 20% calories coming from CHOs. Dr Trudi Deakin has suggested the following: • Less than 136g per day = low CHO diet • Less than 50g per day = very low CHO diet4 This article will not specifically discuss levels of CHO intake needed to induce ketosis. WHAT ARE THE COMMONLY DISCUSSED POSSIBLE RISKS OF A LOW CHO DIET FOR THOSE WITH T2DM?
Increased fat intake The general concern from healthcare professionals in the past is that if little or no energy is coming from dietary CHO, then the diet will be higher in total fat as well as saturated fats and, therefore, the risk of cardiovascular disease will rise further (having T2DM already increases this risk). However, as yet, there is not sufficient evidence to prove either way. www.NHDmag.com November 2017 - Issue 129
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NHD-EXTRA: CONDITIONS & DISORDERS Many high-profile advocates of low CHO diets are sceptical, regarding blood cholesterol levels as an indicator of cardiovascular disease risk and saturated fat in excess of current recommended limits having a negative impact upon health. There are several populations around the world that have been reported to eat almost zero CHOs for the majority of their lives (the Masai in Africa, the Inuit people of the Canadian Arctic), yet maintain a healthy body mass index with low incidence of chronic illness. When this is delved into further, however, some studies do show that the Inuit eat a low CHO diet,9 whereas a literature review of the subject found the Inuit diet to generally consist of around 37% CHO, rising up to 53%. This was found to be the case as early as the 1930s. Heart disease and atherosclerosis have also been found to be relatively common.10 Fibre and wholegrains with a low CHO diet There has been further concern from healthcare professionals regarding reduced fibre intake as a result of a low CHO diet. Provided that people eat a diet abundant in vegetables and around two portions of fruit per day, advocates of low CHO diets protest that this should not be an issue. If, however, somebody very adverse to vegetables embarked on a low CHO diet, this could in theory become a problem. Nutritional inadequacy, particularly in regard to micronutrients A presentation on low CHO high fat diets by Dr Trudi Deakin in June 201511 demonstrated through nutritional analysis that a low CHO high fat diet was nutritionally superior to a high CHO low fat diet in regard to vitamin D, calcium, magnesium, zinc and iron, as well as omega-3 to omega-6 ratio. Much like the argument with wholegrains, if vegetables are eaten in very small amounts, it would make a low CHO diet less nutritionally adequate in regard to some important micronutrients. Low CHO diets and medications If people take medications that have a risk of causing hypoglycaemia to control their diabetes, it is likely that low CHO diets without adequate 60
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supervision from healthcare professionals may cause more incidences of hypoglycaemic episodes and this would only be compounded by increasing physical activity. Low CHO diets lead to low levels of glycogen stored in the muscles and liver. Glycogen is important for people with diabetes as a ‘back up’ for the body when blood glucose falls below normal levels, so not having enough of it increases risk of hypos and can make them more difficult to recover from. Low CHO diets should theoretically be safe if a service user does not take any oral hypoglycaemic agents. WHAT DO THE STUDIES SHOW?
A large percentage of those with T2DM are overweight or obese. Low CHO diets have been found to improve overall weight loss in some studies and are generally seen to be the ‘way to lose weight’ by the mainstream media. Notably, in 2014, General Practitioner Dr David Unwin undertook a pilot study with 19 people with borderline and T2DM over an eight-month period where a low CHO diet was advised (under the supervision of Registered Dietitian Heather Crossley). The results of this small study were hugely positive. In summary: • Blood glucose control improved. • By the end of the study period only two patients remained with an abnormal HbA1c (>42mmol/mol); even these two had seen an average drop of 23.9mmol/mol. • Weight fell significantly (an average of 9kg lost). • Waist circumference decreased from 120.2±9.6 to 105.6±11.5cm (p<0.0001). • Blood pressure improved. • Total serum cholesterol decreased. Only one of the 19 people dropped out of the study because the diet didn’t suit them. When it comes to dietary advice provided, participants were given a small diet sheet of just over 500 words. All starchy CHOs were prohibited and fat is said to be ‘fine in moderation’. This is very different to what is recommended in mainstream media or low CHO diets where fat is extensively promoted without the word moderation being used. A control group was not used in this study.12
A different study including 13 people with T2DM and 13 non-diabetic people found weight loss to be significantly greater for those following a low CHO diet compared to standard healthy eating advice. However, HbA1c and lipid levels did not significantly differ between groups. This was, however, a short study of only 12 weeks with a small sample size.13 A recent meta-analysis of 10 randomised trials (1,376 people in total) showed that low to moderate CHO diets have a greater glucoselowering effect compared with high-CHO diets, even without weight loss. Within this review, it was noted that the greater the CHO restriction within studies, the greater the glucose lowering. This metaanalysis did, however, find that apart from improvements in HbA1c over the short term, there is no evidence regarding superiority of low-CHO diets in terms of glycaemic control, weight, or LDL cholesterol in the longer term (after one year).14 A large systematic review and metaanalysis of 20 randomised control trials found a Mediterranean style diet to improve HbA1c levels more than a low CHO diet, although both induced significant weight loss comparatively to a control group. The Mediterranean style diet contained moderate amounts of carbohydrate.15 Snacking In all of the above studies, snacking has been discouraged. The main reason behind this is that insulin (fat storage hormone) levels and incidence of insulin secretion are aimed to be reduced to improve outcomes of weight loss. Low CHO diets may prove more useful in some people than others Studies overall do show a lot of variability. If somebody has insulin resistance, eating a large amount of CHO and then injecting insulin may not result in inadequate blood glucose lowering as it is the resistance that is the main issue, not the lack of circulating insulin. In these cases, lower CHO (and ketogenic diets) may be more useful to reduce insulin levels as well as excess body fat mass.16,17,18
FINAL THOUGHTS
This area of research is mammoth, complex and difficult to sum up in just a few words. As dietitians, we do know that for a lot of people with T2DM, making small realistic changes that can be stuck with forever has lasting effects. However, there are a large number of people who feel that the age old mantra of ‘eat less and move more’ is simply not enough. Not everyone with T2DM will be the same, and some people have a lot more lifestyle changes that they could employ at baseline comparatively to others with the same HbA1c level. For example, one person may consume a lot of added sugars, large starchy CHO portions, be obese and do little physical activity. Another person with a similar HbA1c reading may already consume under the recommended 30g maximum added sugars per day, eat moderate complex CHO portions, be a healthy weight and be regularly active. A diet with extra emphasis on all sources of CHO may be more beneficial for one of these people than the other. Diabetes UK summed it up well in May this year with an update to their position statement on low CHO diets: ‘The current evidence suggests that low carb diets can be safe and effective for people with Type 2 diabetes. They can help with weight loss and glucose management and reduce the risk of cardiovascular disease. So, we can recommend a low carb diet for some people with Type 2 diabetes. But there is no consistent evidence that a low carb diet is any more effective than other approaches in the long term, so it shouldn’t be seen as the diet for everyone.” 19 As Dietitians, it is our job to not just focus on one nutrient, but look at a client’s overall nutrition, lifestyle, likes and dislikes, cooking skills, medications, readiness to change habits, as well as other health conditions and give dietary advice accordingly. Low CHO diets for the management of T2DM may be more appropriate for some people than others and, in my view, should be utilised accordingly. www.NHDmag.com November 2017 - Issue 129
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