Professor Jim Mann
In the latest issue of The Lancet, one of the world’s leading Medical Journals, the four Otago researchers in human nutrition Professor Jim Mann, Dr Lisa Te Morenga, Dr Rachael McLean and Professor Murray Skeaff, have commented that low carbohydrate diets high in fat (LCHF) continue to attract media attention, despite a substantial body of evidence showing that a range of dietary patterns promote health and reduce risk of chronic disease.
“Whatever the total fat intake, epidemiological, experimental, and clinical trial evidence supports lowering blood cholesterol by partially substituting unsaturated fat for saturated fat. Reduction of conventional cardiovascular risk factors, including blood cholesterol, has contributed to dramatic declines in death rates from coronary heart disease in most western countries during the past 30–40 years.
“Thus, it is a cause for concern that in areas of Sweden where the uptake of LCHF diets has been particularly prevalent, population blood cholesterol levels have risen in parallel with an increase in saturated fat intakes,” they write.
The researchers criticised the justification often given for the use of LCHF diets, pointing out that at typically six-months, they were fairly short in duration. However, trials of at least 12 months’ duration show that compliance with energy restriction is the main determinant of sustained weight loss, with no clear merit of LCHF diets over diets of different macronutrient composition.
They further write that support for LCHF diets has been partly fuelled by the publication of some papers apparently suggestive of benefit.
“Recent evidence, however, confirms the established cornerstones of dietary advice—reduce saturated fat, free sugars, and sodium and increase wholegrain cereals and fibre—although changing disease patterns and additional data have necessitated some changes in emphasis.”
One important change has been the acceptance of a wider range of macronutrients than previously recommended for the prevention and treatment of obesity and associated chronic diseases.
This change has enabled the translation of nutritional recommendations into dietary patterns as diverse as Mediterranean diets, which include up to 40% of energy intake from fat mainly derived from unsaturated vegetable oils, and Asian-style diets, which might contain up to 70% of energy as carbohydrate.
“Whatever the total fat intake, epidemiological, experimental, and clinical trial evidence supports lowering blood cholesterol by partially substituting unsaturated fat for saturated fat.”
However, the group strongly supports the draft recommendations from WHO16 and the UK’s Specialist Advisory Committee on Nutrition (SACN) that intake of free sugars should be radically reduced from present levels of intake.
“Restriction of saturated fat and sodium continues to be advised. Fad diets often arise from the publication of a few studies that seem to contradict conventional wisdom. Urgent headline appeals to overturn dietary recommendations on such limited evidence can harm public health,” they write.