Published: Oct 16, 2014 | Updated: Oct 16, 2014
Bingeing on muffins loaded with saturated fats for 7 weeks raised lipid levels in healthy, normal-weight young adults, but those who gorged on muffins made with polyunsaturated fat improved their plasma lipoprotein profiles, researchers said.
Both groups gained weight in this double-blind, controlled study in humans to examine the cardiometabolic effects of overeating different types of fat, reported David Iggman, MD, of Uppsala University, in Uppsala, Sweden, and colleagues.
They asked 39 people in their 20s and 30s to consume an extra 750 calories a day by eating specially-prepared muffins made with 51% energy from saturated fatty acid (SFA)-rich palm oil or polyunsaturated fatty acid (PUFA)-rich sunflower oil, the authors wrote online in the Journal of the American Heart Association.
There was no significant difference in weight gain, but total HDL (-0.37 versus 0.07, P=0.003), LDL (-0.3 versus 0.05, P=0.007) and apolipoprotein B:AI ratios (-0.07 versus 0.017, P=0.01) decreased in the PUFA versus SFA muffin eaters, they explained.
"Dietary fat composition thus seems to be important during weight gain, which is a novel finding that could have clinical implications in the long term," they wrote.
Earlier results from the same study, published in the July issue of the journal Diabetes, found that excess energy from SFAs promoted liver and visceral fat storage, while additional calories from PUFA promoted lean tissue.
"The current study extends those findings and demonstrates that mean total: HDL cholesterol, LDL:HDL cholesterol, and apoB:apoAI ratios were 13%, 19% and 16% lower during overfeeding PUFA compared with SFA, respectively," the researchers wrote. "We believe this is quite a remarkable difference considering the hypercaloric state."
Proceed With Caution
But Alice Lichtenstein, DSc, a spokesperson for the American Heart Association, said it would be a mistake to conclude from the study that consuming excess calories in the form of PUFAs, or any fat, could be considered healthy.
"These were healthy individuals and they were put in a situation where they were forced to gain weight," Lichtenstein, who is a professor of nutrition science and policy at Tufts University in Medford, Mass., toldMedPageToday. "We would never intentionally do this with people who are overweight or have risk factors for cardiovascular disease."
While warning that the study results could easily be misinterpreted, Lichtenstein said the findings do indicate, as many other studies have, that limiting saturated fats in the diet can reduce cardiovascular risk.
"This adds to the large body of research we have suggesting that unsaturated fats are preferable to saturated fats," she said. "Other than that, one could view this as an interesting study, but I don't think there are many practical implications."
Study Details
While it is clear that moderate weight loss improves metabolic risk, the cardiometabolic consequences of moderate weight gain have not been well studied, the researchers noted.
"The possibility of preventing or reversing cardiovascular disease by dietary interventions has received much interest recently, and the potential anti-atherogenic effects of unsaturated fats in particular," they wrote. "Most dietary interventions, however, have been weight-loss trials or isocaloric trials, the latter aiming at separating the effect of dietary composition from weight change."
Partial replacement of SFA with PUFA has been linked to a moderately reduced cardiometabolic risk in several studies, but it is not known if dietary fat type plays any role during excess calorie consumption and weight gain, the researchers noted.
"Such information would be highly relevant in dietary prevention of obesity-related disorders, especially considering that a large part of the population is overeating and is in chronic positive energy balance," they wrote.
In an effort to better understand the effects of dietary fat composition on lipid levels during weight gain, the researchers conducted a double-blind, randomized, parallel group overfeeding trial using muffins that only differed by fat type.
"We hypothesized that PUFA from sunflower oil could counteract some of the adverse cardiometabolic effects associated with diet-induced weight gain, in comparison with SFA from palm oil," they wrote.
The 39 healthy, normal weight (BMI 18 to 27 kg/m2) volunteers (ages 20 to 38) who took part in the trial were instructed to maintain their normal diets and physical activity level during the 7-week intervention study. In addition to their regular diet, participants consumed 240 calorie muffins (44% energy from carbohydrates, 5% protein, and 51% from fat in palm oil or sunflower oil.
The participants were initially told to eat four muffins a day and muffin count was increased or decreased by one per day depending on the rate of weight gain. The weight gain goal was 3% during the study period, and the main outcomes for the current analysis were numerous cardiometabolic risk factors including systolic and diastolic blood pressure, fasting blood lipoproteins, lathosterol, proprotein convertase subtilisin/kexin type 9, nonesterified fatty acids (NEFA), glucose, insulin, and markers of endothelial function.
Results
The PUFA and SFA groups consumed, on average, 3.2 and 3.1 muffins per day, respectively, during the study and total fat intake increased by 5% in both groups. Body weight increased by 2.2% (1.5 kg or 3.3 lbs), with little difference between groups (P=0.92).
The ratios of total cholesterol to HDL cholesterol, LDL to HDL cholesterol, and apolipoprotein B:AI were lower in the PUFA group and there was no significant difference between groups in total, LDL, or HDL cholesterol, apolipoprotein B or AI, triglycerides, PCSK9, lathosterol, or FGF21 (P≥0.01). However, non-HDL cholesterol tended to be lower during the PUFA versus the SFA diet (P=0.06).
No significant difference was seen between the two groups in markers of endothelial function or inflammation (P>0.14).
Weight gain in the two groups combined was accompanied by a 6% increase in HDL cholesterol (+0.09 mmol/L, P=0.04), without significant changes in other blood lipids. There were also increases in fasting insulin (mean change +17%, +0.91 pmol/L, P=0.003), pro-insulin (21%, 0.73 pmol/L, P=0.007), and homeostasis model assessment of insulin resistance (18%, 0.20, P=0.004). There was no change in fasting plasma glucose.
Study limitations included the trial's short duration and a low power to detect possible differences in some CVD risk factors, meaning that negative results should be interpreted with caution, the researchers wrote. In addition, weight gain among the study cohort did not reach the 3% goal, and the 2.2% weight gain achieved may have been insufficient to affect CVD risk factors in the young, metabolically healthy study population.
Despite the limitations, the researchers concluded that even modest diet-induced weight gain resulting mainly from increased fat intake may promote subclinical endothelial dysfunction and insulin resistance in young, healthy, nonobese people.
"Our study provides novel knowledge by demonstrating improvements in atherogenic lipoproteins when the excess calories are proportionally high in PUFA," they wrote. "This indicates that fat type not only is of importance in isocaloric diets, but also during energy excess and moderate weight gain."
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