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Study Suggests Moderate Fat, Carbohydrate Intake Best for Health

Research on more than 135,000 people across five continents has shown that a diet that includes a moderate intake of fat and fruits and vegetables, and avoidance of high carbohydrates, is associated with lower risk of death.

To define "moderate," the lowest risk of death occurred in those who consumed three to four servings (or a total of 375 to 500 g) of fruits, vegetables, and legumes per day, with little additional benefit from more.

In addition, contrary to popular belief, consuming a higher amount of fat (about 35% of energy) is associated with a lower risk of death compared with lower intakes. However, a diet high in carbohydrates (more than 60% of energy) is related to higher mortality, although not with the risk of CVD.

These are the top messages of two reports published in The Lancet, both produced from a major global study led by researchers at the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences in Hamilton, Canada. The reports were presented at the Congress of the European Society of Cardiology in Barcelona, Spain.

The data are from the Prospective Urban Rural Epidemiology (PURE) study, which followed more than 135,000 people from 18 low-income, middle-income, and high-income countries. The study asked people about their diets and followed them for an average of more than seven years.

The research on dietary fats found that they're not associated with major CVD, but higher fat consumption was associated with lower mortality; this was seen for all major types of fats (saturated fats, polyunsaturated fats, and monounsaturated fats), with saturated fats being associated with lower stroke risk. Total fat and individual types of fat weren't associated with risk of heart attacks or death due to CVD.

The researchers point out that while this may appear surprising to some, these new results are consistent with several observational studies and randomized controlled trials conducted during the last two decades in Western countries.

The large new study, when viewed in the context of most previous studies, questions the conventional beliefs about dietary fats and clinical outcomes, says Mahshid Dehghan, PhD, lead author of the study and investigator at PHRI.

"A decrease in fat intake automatically led to an increase in carbohydrate consumption, and our findings may explain why certain populations such as South Asians, who don't consume much fat but consume a lot of carbohydrates, have higher mortality rates," she says.

Dehghan says that for decades dietary guidelines have focused on reducing total fat to below 30% of daily caloric intake and saturated fat to below 10% of caloric intake. This is based on the idea that reducing saturated fat should reduce CVD risk, but it didn't take into account how saturated fat is replaced in the diet.

She added that the current guidelines were developed about four decades ago using data from some Western countries where fat comprised more than 40% or 45% of caloric intake and saturated fat intakes exceeded 20%. The consumption of these is now much lower in North America and Europe (31% and 11%, respectively).

The second paper from the PURE study assessed fruit, vegetable, and legume consumption and related them to deaths, heart disease, and strokes.

The study found current fruit, vegetable, and legume intake globally is between three and four servings per day, but most dietary guidelines recommend a minimum of five daily servings. Because fruits and vegetables are relatively expensive in most middle-income and low-income countries, this level of consumption is unaffordable for most people in many regions of the world, including South Asia, China, Southeast Asia, and Africa, where the consumption levels are much lower than in Western countries.

"Our study found the lowest risk of death in those who consumed three to four servings or the equivalent to 375 to 500 g of fruits, vegetables, and legumes per day, with little additional benefit for intake beyond that range," says Victoria Miller, MS, a McMaster doctoral student and lead author of the study. "In addition, fruit intake was more strongly associated with benefit than vegetables.

"The PURE study includes populations from geographic regions which haven't been studied before, and the diversity of populations adds considerable strength that these foods reduce disease risk."

Previous research has shown that eating fruits, vegetables, and legumes decreases the risk of CVD and deaths, but most studies were conducted in North America and Europe with few from other parts of the world.

"Raw vegetable intake was more strongly associated with a lower risk of death compared to cooked vegetable intake, but raw vegetables are rarely eaten in South Asia, Africa, and Southeast Asia," Miller says. "Dietary guidelines don't differentiate between the benefits of raw vs cooked vegetables—our results indicate that recommendations should emphasize raw vegetable intake over cooked."

Legumes include beans, black beans, lentils, peas, chickpeas, and black-eyed peas and are frequently eaten as alternatives to meat or some grains and starches such as pasta and white bread.

"Legumes are commonly consumed by many populations in South Asia, Africa, and Latin America. Eating even one serving per day decreases CVD risk and death. Legumes aren't commonly consumed outside these geographic regions, so increased consumption among populations in Europe or North America may be favorable," Miller says.

In a third study published concurrently by The Lancet Diabetes and Endocrinology, the same researchers looked at the impact of fats and carbohydrates on blood lipids and blood pressure.

They found that LDL isn't reliable in predicting effects of saturated fat on future cardiovascular events. Instead, the ratio of Apolipoprotein B and Apolipoprotein A1, or organizing proteins in the blood, gives the best indication of the impact of saturated fat on cardiovascular risk.

Andrew Mente, PhD, an investigator at PHRI and an associate professor in the department of health research methods, evidence, and impact at McMaster, is an author on the three studies.

"The findings of these studies are robust and globally applicable and provide evidence to inform nutrition policies. This is relevant because in some parts of the world nutritional inadequacy is a problem, whereas in other parts of the world nutritional excesses may be the problem," he says.

"Most people in the world consume three to four servings of fruits, vegetables, and legumes a day. This target is likely more affordable and achievable, especially in low- and middle-income countries where the costs of fruits and vegetables are relatively high."

"Moderation in most aspects of diet is to be preferred, as opposed to very low or very high intakes of most nutrients," says Salim Yusuf, DPhil, principal investigator of the study and director of the PHRI.

The PURE study was funded by more than 50 sources, including the PHRI, the Heart and Stroke Foundation of Ontario and Canada, and the Canadian Institutes of Health Research.

— Source: McMaster University