Tabeshpour J, Razavi BM, Hosseinzadeh H. Effects of avocado (Persea americana) on metabolic syndrome: a comprehensive systematic review. Phytother Res. April 10, 2017; [epub ahead of print]. doi: 10.1002/ptr.5805.
Metabolic syndrome is a composite of risk factors including hyperlipidemia, hypertension, hyperglycemia, and obesity that can lead to the development of diabetes and cardiovascular disease. Botanicals may be robust candidates for the alleviation of metabolic syndrome, as they have varying mechanisms of efficacy and bioactivity. Avocado (Persea americana, Lauraceae) is a widely consumed food and contains several classes of bioactive compounds such as phytosterols, previously shown to lower cholesterol concentrations. This systematic review set out to compile data on the efficacy of avocado in alleviating aspects of metabolic syndrome. The authors searched the databases Medline, Scopus, Web of Science, and Google Scholar to yield a total of 129 articles reviewed. No other details about the search methodology are given.
There have been several studies addressing the impacts of avocado consumption on blood glucose concentrations and its regulation. One randomized, clinical trial with 26 overweight patients showed a decrease in insulin and insulin activator glucagon-like peptide-1 with consumption of half of an avocado (no other dosage details are given). Another study in overweight adults reported that an increase in postprandial insulin concentrations 30 minutes after a meal was alleviated when avocado was also consumed. In diabetic (streptozotocin-treated) rats given 1 ml/250 g/day of avocado oil for three months, there was less oxidative stress, lipid peroxidation, and brain triglyceride (TG) concentrations, and there were beneficial effects on brain mitochondrial function. In diabetic rats (alloxan-treated), consumption of water extract of avocado seed at 300 and 600 mg/kg resulted in decreased blood glucose concentrations. Consumption of ethanol extract of avocado leaves also lessened blood glucose concentrations and elevated hepatic glycogen concentrations in diabetic rats (streptozotocin-treated). In a model of rat pancreas in vitro, water extracts of leaves, peel, flesh, and seed showed inhibitory effects on α-amylase (an enzyme that breaks down starch into sugars) and malondialdehyde generation (a marker of oxidative stress).
The potential impact of avocado on dyslipidemia also has been investigated. In a clinical study with healthy subjects consuming avocado as part of a monounsaturated fatty acid-rich diet for two weeks, concentrations of total cholesterol (TC), TGs, and low-density lipoprotein (LDL) cholesterol were decreased, and high-density lipoprotein (HDL) cholesterol concentrations were elevated. In another clinical study, participants with both normal lipid profiles and hyperlipidemia consumed avocado for one week; in both groups, TC, TG, and LDL cholesterol concentrations were significantly less and HDL cholesterol concentrations increased. In a clinical trial in men consuming avocado for eight weeks, TC and phospholipid concentrations were significantly decreased. In female rats fed avocado oil for four weeks, liver lipogenesis and TG synthesis were significantly decreased. Six weeks of avocado seed consumption in rats fed a high-fat diet resulted in lower levels of TC, TGs, and LDL cholesterol, as well as certain liver enzymes. In studies using hyperlipidemic rats, consumption of leaf and fruit extracts of avocado resulted in decreased cholesterol and TG concentrations, and ethanolic seed extract consumption decreased TC, LDL cholesterol, and TG concentrations.
Avocado has also had reported effects on obesity. For example, in overweight subjects in a clinical trial (body mass index [BMI] of 27-44 kg/m2), eating one avocado per day for six weeks resulted in significantly less body weight, BMI, and body fat percentage. This specific effect was also seen in rats fed a high-cholesterol diet and 230 g of avocado pulp for four weeks. In rats fed a high-fat diet, avocado fruit extract consumption at 100 mg/kg/day for 14 weeks resulted in significantly decreased BMI and fat pad mass. Rats fed a high-cholesterol diet and given water and methanol extracts of avocado leaves at 10 mg/kg/day had decreased body weight and liver lipids after eight weeks.
In general, consumption of multiple parts of the avocado plant has resulted in decreased blood pressure in vivo. For example, water extract of avocado at 240, 260, and 280 mg/kg/day resulted in a significant decrease in blood pressure and heart rate in normal rats. Also in a rat model, consumption of water extract of avocado leaves had a slowing effect on heart contraction, a dilatory effect on veins and aorta, and lowered blood pressure.
Of antioxidant assays on avocado seeds, peels, and pulp, seeds were reported to have the highest antioxidant capacity. One safety study is described; in rats fed 2.5 g/kg daily of a water seed extract for four weeks, no impact on body weight or organ:body weight ratios were seen, but fluid intake was significantly increased.
In conclusion, the consumption of avocado may potentially alleviate certain physical aspects of metabolic syndrome; however, additional research into mechanisms of action, appropriate dosage and plant part, and safety assessments is necessary to determine efficacy and tolerability.—Amy C. Keller, PhD