Short, well-controlled trials had suggested regular avocado favorably affects body weight, visceral fat and satiety. Short and well-controlled is also the setting where a food effect most easily appears. So the HAT Trial gave 1,008 people with elevated waist circumference one large avocado a day for six months, against their habitual diet, and measured visceral fat by magnetic resonance imaging. What changed?
Visceral fat did not budge. The change in visceral adipose tissue volume, the , did not differ significantly between the two groups. The estimated mean difference was 0.017 liters, with a P value of 0.405. , high-sensitivity C-reactive protein and the components of metabolic syndrome showed no group differences either. Total and LDL cholesterol fell modestly.
Excess is associated with a raised risk of cardiometabolic disorders, and short, well-controlled clinical trials had suggested that regular avocado consumption favorably affects body weight, visceral fat and satiety. Those trials share a feature worth noticing: tight control over everything the participant eats.
The Habitual Diet and Avocado Trial tested the same idea without that control. It was a multicenter, randomized, controlled parallel-arm trial in which 1,008 free-living individuals with an elevated waist circumference either added one large avocado per day for six months or continued their habitual diet. Magnetic resonance imaging supplied the visceral adiposity measurement.
The primary outcome, change in visceral adipose tissue volume, was not significantly different between the two groups. Nor were the secondary outcomes: hepatic fat fraction, high-sensitivity C-reactive protein, and the components of the metabolic syndrome all came out similar. Body weight, body-mass index, insulin and the cholesterol ratio were similar as well.
What did move was modest. Total and low-density lipoprotein cholesterol showed nominally significant reductions in the avocado group. Read that as an additional outcome rather than a finding the trial was built to test, because a study measuring this many things will turn up some nominal results by chance. The authors conclude that adding one avocado a day for six months did not reduce visceral adipose tissue and had minimal effect on cardiometabolic risk factors.
wat. A thousand people ate an avocado a day for half a year, and the fat around their organs came out the same as everyone else’s.
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This is what happens when a promising short-term food finding gets a large, long, real-world test. The headline effect disappeared, and a small cholesterol benefit was left standing.
How do we know?
Lichtenstein and colleagues ran a multicenter, randomized, controlled parallel-arm trial in which 1,008 free-living adults with elevated waist circumference added one large avocado daily for six months or continued their habitual diet. Magnetic resonance imaging measured the visceral fat.
What is still unknown
The cholesterol reductions were nominally significant additional outcomes, not the primary one, which means they were not the test the trial was designed around and should be treated as a lead.
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