Trimming the fat off dietary guidelines: Study links high carb intake to mortality risk

By Will Chu

- Last updated on GMT

©iStock/egal
©iStock/egal
Global dietary guidelines should be revisited, according to a Lancet study, which found reducing fat intake and replacing it with a high carbohydrate intake may be linked to worse health outcomes.

Findings from a study involving 135,000 people from 18 countries found that high fat diets (about 35% energy - including saturated and unsaturated fats) corresponded to a lower risk of death.

In contrast, a high intake of carbohydrates (above 60% energy) was associated with a higher risk of death.

“Our study provides a global look at the realities of people's diets in many countries and gives a clearer picture of people's fat and carbohydrate intake,"​ said lead author Dr Mahshid Dehghan, senior research associate at McMaster University in Canada.

"The current focus on promoting low-fat diets ignores the fact that most people's diets in low- and middle-income countries are very high in carbohydrates, which seem to be linked to worse health outcomes."

Dr Dehghan’s findings may have more relevance to those living in low- and middle-income countries, located mainly in China, South Asia and Africa. Here, a typical diet consists of more than 65% of energy from carbohydrates.

Dietary guidelines in high-income countries such as the UK recommend a balance of carbohydrates and fats (around 50-55% carbohydrates and around 35% total fat, including both saturated and unsaturated fats).

However, current dietary guidelines set out by the World Health Organisation (WHO) recommend a low-fat diet (less than 30% of energy) and limiting saturated fatty acids to less than 10% of energy intake by replacing them with unsaturated fatty acids.

PURE study

The Prospective Urban-Rural Epidemiology (PURE) observational study tracked the dietary habits of 135,335 individuals, aged 35 to 70 years, from countries across the world from Jan 2003 to March 2013.

These counties included three high-income (Canada, Sweden, and United Arab Emirates), 11 middle-income (Argentina, Brazil, Chile, China, Colombia, Iran, Malaysia, occupied Palestinian territory, Poland, South Africa, and Turkey) and four low-income countries (Bangladesh, India, Pakistan, and Zimbabwe),

Each participant supplied data on socioeconomic status, lifestyle behaviours and medical history. They also completed a questionnaire on the types of foods and beverages they consumed, what size portion and how often.

Follow-up visits for seven and a half years were arranged with the research team to gather additional data on cardiovascular events (fatal and non-fatal heart attacks, stroke and heart failure) as well as incidences of death.

From this information, the researchers were able to calculate rates of cardiovascular events like heart attack, stroke, heart failure, noncardiovascular events and deaths.

Main findings

The team were able to come up with figures describing the average diet (61.2% carbohydrates, 23.5% fat - including 8% saturated fats, 8.1% monounsaturated fats, and 5.3% polyunsaturated fats - and 15.2% protein).

Carbohydrate intake was highest in China (67%), South Asia (65.4%) and Africa (63.3%) whilst total fat intake was highest in North America and Europe (30.5%), Middle East (30.3%), and Southeast Asia (29.2%).

Individually, over 50% of those studies followed a high carbohydrate diet (at least 60% of energy from carbohydrates), with around 25% eating 70% of their daily calories from carbohydrates.

Approximately 50% of those studied took less than 7% of their energy from saturated fats, and 75% ate less than 10% from saturated fats.

The team found diets high in carbohydrates (around 77% energy from carbohydrates) were associated with a 28% higher risk of death, compared with low carbohydrate diets (46% energy from carbohydrates). This equates to 7.2 deaths per 1000 people years, compared with 4.1.

In a similar vein, diets with high total fat intake (35.3% energy from fat) were associated with a 23% lower risk of death, compared with low fat diets (11.0% energy from fat) [4.1 deaths per 1000 people years in people, compared with 6.7].

Rates of major cardiovascular events remained similar for low and high carbohydrate diets and low and high-fat diets.

Despite there being no link to between low carbohydrate intake and health outcomes, the team stressed the findings were not advocating low carbohydrate diets, where carbohydrates made up less than 50% energy.

“A certain amount of carbohydrate is necessary to meet energy demands during physical activity,”​ explained Dr Dehghan. “So moderate intakes, of around 50-55% of energy, are likely to be more appropriate than either very high or very low carbohydrate intakes."

Reaction and response

Responding to the findings, Dr Tom Sanders, professor emeritus of Nutrition and Dietetics at King’s College London, pointed out that the study did not report serum cholesterol concentrations in the different populations.

“This is important because it strongly predicts the 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.”

Dr Sanders also added that the participants from the high-income countries included in this study all had access to good health care.

Susan Jebb, professor of Diet and Population Health at the University of Oxford added: “Only 11% of participants are from Europe or North America and the relevance of this data for UK dietary recommendations is limited.

“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.”

Source: The Lancet

Published online ahead of print: doi.org/10.1016/S0140-6736(17)32252-3

“Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study.”

Authors: Dr Mahshid Dehghan et al.

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