Findings further exonerate fat, and pin blame firmly on "white", refined carbohydrate foods
For decades, most folks — and doctors — believed that fatty diets pile on pounds and promote health problems.
To be sure, any nutrient can be harmful in excess, and that holds true for fats, including saturated ones.
But the evidence never really supported demonization of fats, and evidence in favor of higher-fat/lower-carb diets continues to accumulate.
The results of a huge new global study reinforce the idea that — instead of diets high in fat — diets high in foods featuring "white" refined carbs pose the real threat to heart and overall health.
Its Canadian authors based their findings on diet-health data collected from more than 135,000 people worldwide.
Let's look at those findings, and their implications for the design of healthy diets and goverment diet guidelines.
Huge study finds diets higher in fat, fruits, veggies, and beans healthful
The Canadian team was led by scientists from McMaster University and Hamilton Health Sciences.
They analyzed data from the Prospective Urban Rural Epidemiology (PURE) study, which they'd previously designed and conducted.
The PURE study followed 135,335 people aged 35-70 years living in 18 countries: low-income, middle-income, and high-income (Dehghan M et al. 2017; Miller V et al. 2017).
People were asked about their typical daily diet, and then categorized according to the proportions of their daily calories provided by carbohydrates, fats, and protein.
The researchers followed the participants for more than seven and years, looking for these outcomes:
- Death from any cause
- Death from cardiovascular disease
- Non-fatal heart attacks, stroke, or heart failure
Secondarily, the participants’ health records were examined for these outcomes:
- All heart attacks and stroke
- Death from cardiovascular disease
- Death from causes other than cardiovascular disease
Key findings of the PURE study
These diet patterns were linked to reduced risk of death and/or heart disease:
- Moderate-high fat intake
- 3-4 daily servings of fruits and veggies
- Eating few refined, grain-source carbohydrates
Compared to lower fat intakes, consuming relatively high amounts of fat — about 35 percent of daily calories — was linked with a lower risk of death.
Critically, this risk reduction applied to higher intakes of all types of fat — saturated, polyunsaturated, and monounsaturated — with saturated fats linked to lower risk for stroke.
Contrary to conventional wisdom, the findings did not link higher total fat intake or higher intakes of particular fats to higher or lower cardiovascular risks.
In contrast, diets high in refined, grain-source carbohydrates (more than 60 percent of daily calories) were linked to a higher risk of death, although not to a higher risk for cardiovascular disease.
The lowest risk of death was seen in people who reported eating three to four servings (375-500 grams or 13-18 ounces) of fruits, vegetables and beans daily.
Compared with high vegetable intake, high fruit intake was linked even more strongly to reduced health risks.
Somewhat surprisingly, the analysis found little additional risk-reduction among people who reported eating more than three to four servings of fruits, vegetables, and beans daily.
Findings further undermine demonization of fat and saturated fat
For decades, most dietary guidelines have called for keeping total fat below 30 percent of daily calories, and saturated fat below 10 percent.
Those guidelines rested on shaky, largely discredited evidence that fat promotes weight gain, and that saturated fat promotes cardiovascular disease.
Cholesterol levels matter, but the picture is usually oversimplified, as the authors of the PURE study confirmed in a separate study (see "Related Blood Fats study", below).
Saturated fats vary in their effects on cholesterol, and they include apparently benign kinds like stearic acid, which predominates in cocoa butter (chocolate) and beef.
And the evidence that replacing saturated fats with polyunsaturated fats from vegetable oils aids heart health is surprisingly weak — due to problems with the design and analysis of many studies on the subject (see Vegetable Oils Debunked for Heart Disease and its links to related reports).
Official diet guidelines first appeared about four decades ago, when fat intake in Western countries averaged more than 40 to 45 percent of calories, and saturated fat accounted for about half of total fat intake.
The constant drumbeat of fat-demonization drove fat consumption lower, to about 31 percent of daily calories from total fat, and 11 percent from saturated fat.
Unfortunately, many people replaced dietary fat with refined carbohydrates, often from junky processed foods.
The PURE study's findings highlight the folly of the low-fat craze that held sway during the 1990s and beyond.
As lead author Mahshid Dehghan, Ph.D., said, “… our findings may explain why certain populations … who do not consume much fat but a lot of carbohydrates, have higher mortality rates.”
What do the findings mean, and are they really news?
The results may seem unsurprising to folks familiar with the evidence — including our readers — but they’re worth noting for three reasons:
- The study was very large and statistically sound.
- Its findings reinforce those from similar studies conducted in recent years.
- It covered many lower-income nations, but its findings held true across people in different lands with widely varying incomes.
Epidemiological studies like this one cannot prove cause-effect relationships between foods or nutrients and health outcomes
High quality clinical trials can yield accurate results far more reliably than epidemiological studies can — but they remain fairly rare, thanks to the large numbers, long periods, and deep pockets required.
That said, when the findings of large epidemiological studies match, attention must be paid — especially if they're support by clinical trials, as is the case here
For example, a trial from George Washington University compared lifestyle interventions — exercise plus a plant-based, whole foods diet — with metformin, a standard diabetes prevention and treatment drug (Knowler WC et al. 2002).
The results — like those of the PURE study — showed that a diet high in vegetables, fruits, and nuts (plus two hours of weekly exercise) outperformed metformin at controlling diabetes.
Co-author Andrew Mente made a good point about the strength of the PURE study findings and their implications:
“The findings of these studies are robust, globally applicable and provide evidence to inform nutrition policies … in some parts of the world nutritional inadequacy is a problem, whereas in other parts excesses may be the problem.”
What the PURE study says about fruits, vegetables, and cooked vs. raw
The PURE study also compared people’s fruit, vegetable and legume (bean/lentil) intakes to the risk for death, heart disease, and stroke over the course of seven-plus years.
While most dietary guidelines recommend five daily servings of fruits and vegetables, the study participants' combined intakes of fruits, vegetables, and legumes (beans) ranged between three and four servings per day.
As study co-author Andrew Mente said, “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.”
Previous research has shown that eating fruits, vegetables and legumes reduces risks for cardiovascular disease and deaths — but most studies were conducted in North America and Europe.
Doctoral candidate Victoria Miller, lead author of the produce-and-health report, stressed this aspect of the new findings: “The PURE study includes populations from geographic regions which have not been studied before, and the diversity of populations adds considerable strength that these foods reduce disease risk.”
Miller’s team also looked at the effects of raw versus cooked vegetables, and as she said, “Raw vegetable intake was more strongly associated with a lower risk of death compared to cooked vegetable intake...”.
Beans and lentils: Good stuff, despite Paleo plaints
Some, not all, advocates for Paleo diets — i.e., grain-free diets high in meats, fish, fruits, nuts, and vegetables — reject beans and lentils.
Yet we now know that paleolithic (stone age) Neanderthal people ate wild legumes and that the reasons usually given for barring beans from Paleo diets don’t stand up to scrutiny.
Legumes include beans, lentils, peas, chickpeas and black-eyed peas, which in lower-income countries often replace costlier animal sources of protein.
Beans provide beneficial polyphenol antioxidants like those found in colorful produce — as well as “resistant” starch, which stabilizes blood sugar for hours after eating a meal that includes beans.
As Dr. Miller said, “Eating even one serving [of legumes] per day decreases the risk of cardiovascular disease and death … increased consumption among populations in Europe or North America may be favorable.”
Related blood-fats study undermines cholesterol/saturated-fat myths
Separate from their PURE study, the same Canadian team scrutinized the impact of fats and carbohydrates on blood lipids (fats and cholesterol) and blood pressure.
They found that blood levels of LDL (so-called “bad” cholesterol) do not reliably predict the effects of dietary saturated fat on the risk for adverse cardiovascular events like heart attacks.
Instead, the amounts of two other cholesterol-carriers in your blood — the ratio of Apolipoprotein B (ApoB) to Apolipoprotein A1 (ApoA1) — predicts the impact of saturated fat on cardiovascular risk far more accurately.
That finding fits with the new, far more nuanced picture of the heart-health impacts of people's cholesterol profiles.
The devil of any doctor-patient discussion of cholesterol lies in the details, which too often go unexamined.
- Dehghan M et al.; Prospective Urban Rural Epidemiology (PURE) study investigators. Associations of fats and carbohydrate intake with cardiovascular disease and mortality in 18 countries from five continents (PURE): a prospective cohort study. Lancet. 2017 Aug 28. pii: S0140-6736(17)32252-3. doi: 10.1016/S0140-6736(17)32252-3. [Epub ahead of print]
- Florez H, Pan Q, Ackermann RT, Marrero DG, Barrett-Connor E, Delahanty L, Kriska A, Saudek CD, Goldberg RB, Rubin RR; Diabetes Prevention Program Research Group. Impact of lifestyle intervention and metformin on health-related quality of life: the diabetes prevention program randomized trial. J Gen Intern Med. 2012 Dec;27(12):1594-601. doi: 10.1007/s11606-012-2122-5. Epub 2012 Jun 13.
- Herman WH, Hoerger TJ, Brandle M, Hicks K, Sorensen S, Zhang P, Hamman RF, Ackermann RT, Engelgau MM, Ratner RE; Diabetes Prevention Program Research Group. The cost-effectiveness of lifestyle modification or metformin in preventing type 2 diabetes in adults with impaired glucose tolerance. Ann Intern Med. 2005 Mar 1;142(5):323-32.
- Knowler WC, Barrett-Connor E, Fowler SE, Hamman RF, Lachin JM, Walker EA, Nathan DM; Diabetes Prevention Program Research Group. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med. 2002 Feb 7;346(6):393-403.
- McMaster University. International study shows moderate consumption of fats and carbohydrates best for health. August 29, 2017. August 29, 2017, Accessed at https://www.eurekalert.org/pub_releases/2017-08/mu-iss082517.php
- Miller V et al.; Prospective Urban Rural Epidemiology (PURE) study investigators. Fruit, vegetable, and legume intake, and cardiovascular disease and deaths in 18 countries (PURE): a prospective cohort study. Lancet. 2017 Aug 28. pii: S0140-6736(17)32253-5. doi: 10.1016/S0140-6736(17)32253-5. [Epub ahead of print]
- Tuomilehto J, Lindström J, Eriksson JG, Valle TT, Hämäläinen H, Ilanne-Parikka P, Keinänen-Kiukaanniemi S, Laakso M, Louheranta A, Rastas M, Salminen V, Uusitupa M; Finnish Diabetes Prevention Study Group. Prevention of type 2 diabetes mellitus by changes in lifestyle among subjects with impaired glucose tolerance. N Engl J Med. 2001 May 3;344(18):1343-50.