Consumption of extra virgin olive (Olea europaea, Oleaceae) oil (EVOO), rich in the monounsaturated fatty acid (MUFA) oleic acid, has been shown to reduce the risk of cardiovascular disease (CVD). Risk of CVD has been associated with excess body fat, and both conditions have been linked with metabolic syndrome. Use of EVOO for weight control rests on epidemiological observations that a “Mediterranean diet,” rich in olive oil, is significantly less likely than other diets to promote obesity. However, such diets have many functional low-density foods. Randomized clinical trials (RCTs) have been inconclusive. “Good fats” in energy-restricted low-fat diets have been shown to improve taste and compliance, but there is no clear evidence of EVOO’s effects on body weight/fat loss. In this double-blinded, placebo-controlled RCT, EVOO was compared to soy (Glycine max, Fabaceae) bean oil in women with excess body fat.
Of 753 recruited through advertisements in Viçosa, Minas Gerais, Brazil, site of the Universidade Federal de Viçosa, 77 from 19-41 years of age were randomly assigned to 2 groups. Included subjects had >32% body fat (normal range for women of this age is 25-31%); mostly used soybean oil to cook; and were nonsmokers, not pregnant, and not lactating. Exclusion criteria were drinking alcohol >15 g/d, being elite athletes (>10 hrs exercise/week), habitual use of olive oil (>8 mL/d), recent diet or exercise changes, use of supplements or drugs except contraceptives, allergy/aversion to test ingredients, and gastrointestinal or other acute or chronic disease besides obesity. Of those randomly assigned, 16 dropped out before the intervention—11 from the control and 5 from the EVOO group, leaving 28 in the former and 33 in the latter. Of these, 3 from the control group dropped out during the RCT, as did 7 from the EVOO group, leaving 25 in the control and 26 in the EVOO group to complete the intervention. Data from 5 of those in the control and 5 in the EVOO group were excluded from the analysis, leaving 41 subjects. Retrospective power calculations showed that 21 subjects were sufficient to detect increments of −1.09 kg body fat in the EVOO group. An increment of −1 kg body fat was considered relevant.
The RCT lasted 9 weeks ± 5 days to prevent hormonal interference. For 1 week before the intervention, subjects refrained from olive oil and alcohol but maintained other dietary and activity habits. The night before the intervention began, subjects ate a standard dinner. They were tested for anthropometric, body composition, and blood pressure measured at baseline and on the last day of the RCT, including weight, height, and body mass index (BMI). Waist, hip, neck, and thigh circumference and sagittal abdominal diameter also were measured at those times. Waist/hip ratio and conicity index were calculated. Blood pressure was taken in both arms. Dual-energy X-ray absorptiometry (DXA) scan assessed lean mass, total body fat, and fat distribution. Blood was analyzed for serum glucose, total cholesterol, triglycerides (TG), high-density lipoprotein cholesterol (HDL-c), low-density lipoprotein cholesterol (LDL-c), uric acid, urea, creatinine, alkaline phosphatase (AP), aspartate aminotransferase, alanine aminotransferase, γ-glutamyltransferase, serum very-low-density lipoprotein cholesterol, and serum insulin. Insulin resistance and atherogenic index (TG:HDL-c) were calculated. Levels of pro-inflammatory interleukin (IL)-8, IL-1β, IL-10, IL-12p70, and tumor necrosis factor-α (TNF-α) were measured. Participation was delayed for any inflammation or intestinal disorder at baseline.
After assessment and each succeeding day, subjects had a breakfast with 300 mL of a high-fat milk-derived flavored drink containing 25 mL of either soybean oil (Corcovado®; Archer Daniels Midland; Uberlândia, Brazil) or EVOO (Andorinha®; Sovena S.A.; Algés, Portugal), according to the group. The milk-derived drink, served in the laboratory on weekdays and provided for subjects’ weekend use at home, was the same for both groups except for oil content. Two low-fat cookies also were offered. Breakfast meals had a rotating menu of 6 “breakfast flavors” with similar nutritional composition, to avoid monotony and to improve compliance. Each subject was prescribed an individual energy-restricted low-fat diet for other meals. Energy requirements for overweight/obese women were calculated and caloric restriction applied, with coefficients for sedentary and low-active women. There were no differences between groups in diets’ energy or macronutrient content. No high-MUFA food, other than the breakfast EVOO for the EVOO group, was included. Food diaries were used on 3 non-consecutive days before and during the RCT.
Per-protocol analyses were used since many subjects were lost after randomization. Body weight and BMI fell in both groups but the EVOO group lost more total fat than control (−2.4 ± 0.3 kg, 95% confidence interval [CI] −3.1 to −1.73 kg vs. −1.30 ± 0.40 kg, 95% CI −2.21 to −0.44 kg; Pinter=0.037). [Note: In the article text, this result is presented in reverse order.] Fat loss was 80% greater in the EVOO group. This is the first clinical evidence that EVOO increases fat loss from energy restriction even in a non-Mediterranean diet. Both groups had decreases in all anthropometric variables except waist/thigh ratio [referred to as waist/hip index in Suppl. Table 2]. Both had reductions in total fat and at specific fat sites, but not lean mass. Lean mass did not change in control but increased in the EVOO group (Pinter=0.195). Serum glucose fell in both groups. In the control group only, HDL-c was reduced and IL-10 increased. Creatinine rose and AP fell in the EVOO group only, with a trend toward reduced IL-1β (P=0.060). Diastolic blood pressure fell only in the EVOO group and rose slightly in control (−5.05 ± 1.60 mmHg, 95% CI −8.39 to −1.70 mmHg vs. +0.25 ± 1.16 mmHg, 95% CI −2.18 to 2.68 mmHg; Pinter=0.011). [Note: In the article text, this result is presented in reverse order. The report is marred by further text errors, e.g., attributing downregulation of inflammatory pathways to increased consumption of α-linolenic acid—exactly the opposite of this trial’s results.]
While the results of this clinical study are promising, and consideration of EVOO in a healthy diet is warranted, further evidence is needed to support the use of olive oil for the reduction of excess body fat.
Galvão Cândido F, Xavier Valente F, da Silva LE, Gonçalves Leão Coelho O, Gouveia Peluzio MdC, Gonçalves Alfenas RdC. Consumption of extra virgin olive oil improves body composition and blood pressure in women with excess body fat: a randomized, double-blinded, placebo-controlled clinical trial. Eur J Nutr. August 14, 2017; [epub ahead of print]. doi: 10.1007/s00394-017-1517-9.