August 29, 2017

expert reaction to study of replacing fat with high carb intake

Publishing in the The Lancet, researchers have looked at the high fat diets versus high carbohydrate diets across 18 countries and reported worse health outcomes in those with high carbohydrate diets.

Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“The study is a large observational study that aimed to compare cardiovascular disease incidence and mortality with dietary fat intake between high income, middle income and low income countries in men and women aged 35 – 70 years. The study failed to show any effect of fat intake on this outcome – death from stroke (which is related to high blood pressure) was as common as that from myocardial infarction (which is related to serum cholesterol). Unfortunately, the study did not report serum cholesterol concentrations in the different populations, which is important because it strongly predicts incidence of myocardial infarction in younger age groups. In North America, Australasia and Northern Europe the rates of stroke have been falling strongly for many years and the relative incidence of stroke is much lower than myocardial infarction under the age of 70 years.

“Overall, the incidence of cardiovascular disease events was low in the participants of this study around 4/1000 per year compared with 7/1000 in a UK non-smoking male or 4/1000 in a female of the same age (56) with the same blood pressure (the risk would be double in smokers).

“The authors conduct some modelling to suggest that countries that eat more carbohydrate than fat are at greater risk of dying from cardiovascular particularly when intakes are very high and an intake of 35% energy is associated with the lowest risk of cardiovascular disease but statistically this should not be done as the primary analysis showed no effect of fat.

“The instrument used to estimate fat intake which was adapted from a US food frequency questionnaire is also likely to underestimate fat intakes and depends on assumptions about portion sizes being similar between different countries and the composition of food being similar to those reported in US tables.  The high income countries included in this study were Sweden, Canada and the UAE where the participants had access to good health care. The inclusion of UAE in this group of high income countries is odd given the known extremely high rates of diabetes in. Even in these high income countries intakes of fat and saturated fat were low and in most cases met recommendations for saturated fat (no more than 10% energy). The authors claim that current recommendations suggest that total fat should provide less than 30% energy, which they term low fat. However, current, recommendations including those in EU and US dietary guidelines give an acceptable intakes of fat intakes from 25% to 35% of the energy.  The cohorts from China, South Asia and Africa all had fat intakes below current WHO/FAO recommendations 25% – 35% energy.

“The authors report that overall mortality rates were higher in the lower income countries and that this was associated with lower intakes of fat and protein and higher intakes of carbohydrates.

“The accompanying editorial suggests that this provides evidence to challenges the definition of a healthy diet in Western countries which is not really relevant to the research question for low and middle income countries which are suffering from the double burden of malnutrition – a high risk of non-communicable diseases as well as nutritional deficiencies. Nutritional inadequacy is more likely on diets providing less than 25% energy and it is recognised that there a need to increase the proportion of energy from fat in low income countries particularly if it is derived from nutrient dense foods such as legumes, nuts, and animal products rather than oils added to starchy foods. As a point of information, fat currently provides 35% of the energy in both the UK and the USA. A high fat diet would be one providing more than 40% energy. The data from South East Asia in this context are interesting as life-expectancy has increased greatly in the past couple of decades where there have been major improvements in public health and diet. This study show total fat and saturated fat to be 29.2% and 9.2% of the energy respectively in South East Asia, based mainly on Malaysia, are within the current recommendation of WHO/FAO compared with much lower intakes in China, Bangladesh and India where there is still overdependence on white rice.”

Prof Susan Jebb, Professor of Diet and Population Health at the University of Oxford, said:

“This paper considers the relationship between diet and health outcomes for predominately low and middle income countries (15 out of 18 countries studied) where the pattern of disease is very different from that observed in the UK.

“It found that a high proportion of carbohydrate in the diet (more than about 60% of energy) was associated with higher death rates. Most of the current debate about diet and health has focused on cardiovascular mortality, but there were no significant associations between carbohydrate intake and major cardiovascular diseases. The apparent excess mortality among those consuming high carbohydrate diets was from non-cardiovascular deaths and is unexplained.

“Only 11% of participants are from Europe or North America and the relevance of this data for UK dietary recommendations is limited. The background diet of most of the countries in this analysis is very different from the UK. For example, here only the highest quintile (top 20%) of dietary fat intake reaches the average intake for the UK and the lowest quintile (bottom 20%) of carbohydrate is close to the UK average. There are many other non-diet related factors which contribute to differences in ill-health and the causes of death.  It is quite possible that the higher mortality observed in this study in groups consuming a high proportion of energy from carbohydrate and less from fat, reflects differences in socio-economic status that cannot be adequately removed from the statistical analysis of the relationship between diet and health outcomes.

“In their press release the authors remark “The best diets will include a balance of carbohydrates and fats – approximately 50-55% carbohydrates and around 35% total fat, including both saturated and unsaturated fats.” This is a thumbs-up for UK recommendations which advise up to 35% energy from fat and an average of 50% energy from carbohydrate (of which only 5% should be sugar).”

Declared interests:

None declared