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Low Carbohydrate High Fat Diets

The evolution of low carb
In recent times the low carbohydrate trend has evolved from a short term weight loss diet to being promoted as a long term “lifestyle”.

In line with this trend, the low carbohydrate high fat (LCHF) lifestyle has emerged as the latest diet philosophy being hailed in the media as the secret to long term weight loss, health and wellbeing. In fact, some LCHF proponents are now calling for all Australians to adopt a LCHF eating pattern, which represents a radically different diet to those recommended within evidenced based Australian and International Dietary Guidelines.

Here we explore the LCHF diet, review the evidence behind some of the recent headlines and discuss how a LCHF eating pattern stacks up against evidenced based guidelines which promote adequate nutrition and reduced risk of disease over the lifespan.

What is a LCHF diet?
Due to the similarities with ‘Paleo style diets’ LCHF dieters often use the terms interchangeably or in concert when describing their diet philosophy.

The purpose of a LCHF diet is to achieve state of ‘ketosis’. This occurs when the body is starved of its primary fuel source (carbohydrates) and so is forced to use dietary fats as an alternative source of energy via ketosis.(7) Supporters of LCHF diets claim an eating pattern that imposes a metabolic shift towards ketosis reduces the risk of heart disease, diabetes and obesity as well as improves appetite control, weight management, immunity, sustained energy and mental alertness.(1-5)

As the name suggests, LCHF diets are characterised by very low carbohydrate intakes, generally less than 50g/day which is achieved through the elimination of selected foods from the five food groups including grain foods including whole grain or high fibre grain foods, legumes, fruit, low fat diary and starchy vegetables.(1-3) In addition, similar to the Australians Dietary Guidelines, LCHF dieters are instructed to limit or avoid discretionary choices such as sweetened beverages, cakes, biscuits, pastries and other carbohydrate containing discretionary food choices.

As a result LCHF diets contain relatively higher intakes of fat and protein through an abundance of dietary fats and oils, meats (often including processed meats such as bacon, sausages), seafood, eggs, nuts, seeds and full fat dairy. A typical LCHF daily meal plan recently published by advocates of LCHF diets delivers around 10,500kJ of energy,  42g carbohydrates (7% total energy), 20g fibre, 204g total fat (~72% total energy), 81g saturated fat (28% total energy), 78g monounsaturated fat and 28g polyunsaturated fat and 134g protein (~22% total energy).(3, 6)

To put this in context, the 2013 Australian Dietary Guidelines were developed using the NHMRC Nutrient Reference Values (NRV’s) for macronutrients. These NRV’s are expressed as a percentage contribution of carbohydrate, protein and fat to daily energy intake (carbohydrate 45-60%: fat 20-35%: saturated fat no more than 10%: protein 15-20%). These NRVs provide the macronutrient ranges upon which the Australian Dietary Guidelines to ensure these recommendations allow a wide range of dietary patterns, which provide all of the essential nutrients and promote health.

Based on this analysis it’s clear that LCHF eating patterns are radically different to those endorsed by the Australian Dietary Guidelines and it follows that elimination of carbohydrate rich food groups also translates to lower intakes of the essential nutrients and health protective components these foods deliver. Indeed the example LCHF daily meal plan outlined above is lower in fibre than the adequate intake NRV and is significantly lower than the Suggested Dietary Targets (SDTs) for fibre recommended for reduced risk of chronic disease.

The latest science on LCHF
As with all science there is constantly new research being conducted leading to scientific debate. While it is important to consider the findings of new research, this must be done in the context of all the research in the area and not in isolation of single studies. As such systematic analysis of the total body of evidence is vital to guide the practise of health care professionals as is the critical analysis of new research to ensure that the findings are fair, unbiased and relevant in the real world.

With this in mind; in regards to weight management, while there is limited evidence that LCHF may offer short term benefits, robust scientific analysis including a recent meta-analysis consistently demonstrates that low carbohydrate or LCHF diet do not offer any long term weight loss benefits compared with an energy matched balanced diet.(7, 8)

A recently published trial which generated the headline in the New York Times “A Call for a Low-Carb Diet That Embraces Fat” clearly illustrates why critical analysis of new research is important. The study behind this headline was a 12 month trial of 148 obese people which compared a LCHF diet versus a higher carbohydrate diet and their respective effects on weight and heart health.(9) When interpreting studies which compare low carbohydrate diets versus a higher carbohydrate, it is important to keep in mind that not all carbohydrate foods are equal. As such it is important to examine the actual food choices and nutrient intakes of study participants to determine whether a low carbohydrate diet compared against a higher carbohydrate diet which actually reflects dietary guidelines, which emphasise nutrient and fibre rich carbohydrate foods.

This trial did not provide detail on the actual food choices of people on the higher carbohydrate diet, which was intended to reflect dietary guidelines. As many carbohydrate foods restricted on a LCHF diet are also fibre rich, it would be fair to assume the fibre intakes of the people on this diet would be significantly higher compared with a LCHF diet. However, in this study fibre intakes were almost identical and much lower than recommended intakes, with daily averages of 15g and 16g for the LCHF and higher carbohydrate diet respectively. This tells us that on average the higher carbohydrate group were not consuming fibre rich sources and so the group upon which the LCHF has been compared is unlikely reflective of a dietary guidelines. Given this analysis, it’s not surprising that those following the LCHF diet, which represented a radical change in diet, consumed less energy, losing more weight over 12 months and so experienced greater improvements in heart health when compared with a diet which did not reflect a healthy higher carbohydrate diet.

This limitation and others highlighted here by Dr David Katz, Director of the Yale Prevention Research Centre demonstrate the importance of the critical analysis of new research. As well as identifying critical flaws in the study design Dr Katz noted important factors for establishing a long term eating pattern which are commonly ignored in such studies including “Was the diet sustainable? Could families join in? Would the diet reliably improve health and prevent disease across a lifespan?”.

As Dr Katz points out, when it comes to achieving or maintaining a healthy weight the best approach is to establish an eating pattern and lifestyle which you can live with for a lifetime. In contrast a LCHF diet restricts many nutritious, affordable and culturally and socially acceptable foods and is yet to be proven to promote health in the long term.

In addition to research on weight management and heart health researchers have investigated the short term impact of LCHF diets on blood glucose control. In people with diabetes or an increased risk of diabetes a number of recent trials have reported positive outcomes of LCHF diets in the short term.(10, 11) Indeed, some researchers have cited such trials and challenged the current best practice guidelines for the treatment of diabetes in adults, making the case that low carbohydrate ketogenic diets as the primary dietary therapy.(12)

Despite this recent evidence, it should be noted that the evidence is limited and that the best practice guideline updated in 2013, provide recommendations based on the total body of evidence indicate that for improved blood glucose control for adults with diabetes as well as adequate nutrition and reduced risk of disease, macronutrient intakes should be individualised within the ranges which guide nutritionally balanced dietary guidelines.(13)

Potential long term risks of LCHF 
While there is some limited evidence of short term health effects of a LCHF diet, as a long term eating pattern LCHF diets are yet to be proven to provide adequate nutrition, be sustainable and prevent disease across the lifespan.

In contrast there is evidence that lower carbohydrate intakes in the long term may pose health risks. A 2013 meta-analysis found that compared with high carbohydrate intakes, long term low carbohydrate intakes  were linked with an increased risk of an early death in humans by 30%.(14) This observation has since been supported by a comprehensive study in animals; not possible in humans due to its complexity and for ethical reasons, which found that mice consuming a higher carbohydrate diet experienced a 30% increased life span and better health compared to mice consuming lower carbohydrate intake.(15)

LCHF diets may also negatively impact risk of heart health and type 2 diabetes through restriction of nutrient and fibre rich whole grains, high fibre grain foods and legumes.(16-23) And the abundance of saturated fat(3) observed in LCHF diets also contradicts recommendations from heart health authorities around the world who advise people to restrict intake of saturated fat in favour of polyunsaturated fat.(21, 24-26)

With respect to reducing cancer risk, LCHF diets do not align with key recommendations from the World Cancer Research Fund. LCHF diets appear to fall short of providing adequate fibre yet dietary fibre, particularly cereal fibre protects against bowel cancer, Australia’s second biggest cancer killer.(27, 28) The World Cancer Research Fund also cautions against high intakes processed meats which may be observed in a LCHF eating pattern due to the link between these foods  and some cancers.(27)

While the long term impact of a LCHF on disease and longevity is unknown, the 2013 Australian Dietary Guidelines are based on over 55,000 studies, demonstrates that an eating pattern relatively higher in good quality carbohydrate foods such as whole grains, high fibre grain foods, legumes, fruit and vegetables, moderate in protein and lower in saturated fats delivers adequate nutrition and reduces risk of diet related disease over the lifespan.(21)

The Bottom Line: Bring back the balance
Surveys indicate Australians are choosing discretionary grain foods more often than is recommended and are not choosing whole grain and high fibre grain foods often enough. Rather than following a fad diet, the total body of scientific evidence shows people would benefit from eating less discretionary foods and choosing whole grain and high fibre grain foods more often as part of a balanced diet.

In support of the evidenced based 2013 Australian Dietary Guidelines, GLNC encourages Australians to enjoy grain foods 3-4 times each day, choosing at least half as whole grain or high fibre and aiming to eat legumes at least 2-3 times each week.

References: 

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