Plants do not synthesize cholesterol. The plant versions of cholesterol are substances collectively known as plant sterols, such as lathosterol, campesterol and beta-sitosterol. They’re structurally similar to cholesterol, and studies show that they can displace cholesterol in the human body. So taking them in will promote the excretion of the cholesterol you get from food, which would have the effect of reducing cardiovascular disease. What if you combined plant-sterol intake with aerobic exercise, which also has established credentials for cardiovascular protection? Would the combination be more effective than either alone?
That was the focus of a recent study.1 It lasted eight weeks and featured 84 human subjects randomly assigned to one of four groups: 1) combination of sterols and exercise; 2) exercise; 3) sterols alone; 4) control, no exercise or sterols. The sterols-alone group decreased total blood cholesterol by 8.2 percent compared to starting measurements. The plant sterols also lowered low-density-lipoprotein (LDL) cholesterol, elevated levels of which are a risk factor for cardiovascular disease.
Exercise alone increased beneficial high-density-lipoprotein (HDL) cholesterol by 7.5 percent, while decreasing blood triglycerides, or fat, by 13.3 percent from baseline. Bodyfat levels in those subjects also declined an average of 3.9 percent from the aerobic exercise after eight weeks. The big news, however, is that the combination of plant sterols and aerobic exercise worked better in lowering all cardiovascular risk factors than either intervention alone.
Plant sterols were at one time promoted as ‘testosterone precursors.’ That was based on two things. First, the raw material for testosterone synthesis in the body is cholesterol, which is converted through several enzymatic steps into testosterone. But the human body cannot do the same conversion for plant sterols because it lacks the necessary enzyme. It can, however, be done under lab conditions. The second reason for promoting plant sterols as testosterone boosters was the similarity in name between ‘sterols’ and ‘steroids.’ In reality, that similarity was all the two substances had in common, other than being similar in structure to cholesterol.
Besides being useful for the prevention of cardiovascular disease, plant sterols can help prevent prostate gland enlargement. In fact, the active ingredients in saw palmetto, which is often used to prevent prostate problems, are various plant sterols.
On the negative side animal-based studies and a few human studies have linked a heavy intake of plant sterols to lowered testosterone levels. That likely has something to do with displacing cholesterol in reactions where cholesterol is used to synthesize testosterone in the body. The good news, though, is that you would need to ingest megadoses of plant sterols to induce any type of testosterone-inhibiting activity.
1 Varady, K.A., et al. (2004). Plant sterols and endurance training combine to favorably alter plasma lipid profiles in previously sedentary hypercholesterolemic adults after eight weeks. Am J Clin Nutr. 80:1159-66.