Intimal Thickening in Normocholesterolemic Rhesus Monkeys Fed Low Supplements of Dietary Cholesterol, Circulation Research, 1974
Rhesus monkeys were fed a high-fat diet containing either 0, 43, or 129 micrograms/kcal of cholesterol a day for 18 months. There was a cholesterol-free control group:
- Control: No cholesterol
- Group 1: about 25.8 milligrams cholesterol (~86mg chol for a human eating 2000 kcal, about half a small egg)
- Group 2: about 77.4 milligrams cholesterol (~258 chol for a human, about 1 jumbo egg)
- Group 3: about 232.2 milligrams cholesterol (~774 chol for a human, about 3 extra large eggs)
After 18 months, addition of dietary cholesterol increased plasma cholesterol in all groups; increases were evident within the first 2 weeks:
- Group 1: Baseline cholesterol:115 mg/dl, After 18 months: 130mg/dl
- Group 2: Baseline cholesterol:117 mg/dl, After 18 months: 168mg/dl
- Group 3: Baseline cholesterol:115 mg/dl, After 18 months: 392mg/dl
Since Group 3's total cholesterol rose so high, they were excluded from further analysis.
"A decrease in HDL and an increase in LDL cholesterol occurred after cholesterol feeding."This first photo, Figure 5, was from the group receiving the human equivalent of 86mg cholesterol, or what you get in about a half of a small egg. I was surprised there was this much narrowing in just 18 months:
"Clearly elevated lesions [on the aorta] were positively identified only in the [cholesterol-fed] monkeys."
"The [cholesterol-fed] monkeys had more intimal thickening expressed as cross-sectional area than did the control group. ... The involved areas contained significant fibrous and lipid elements. Foam cells were seen to a variable and sometimes prominent degree."
"The monkeys fed the higher amount of dietary cholesterol showed an increase in hepatic [liver] cholesterol."
"The fact that lipid absorbed from the gut enters the arterial wall is well established." (They discussed this.)
This point was notable:
"The regimen for group 1 was originally designed to demonstrate a null point of the effect of dietary cholesterol on the arterial intima. However, such a point was not found; no threshold for dietary cholesterol was established with respect to a putatively adverse effect on arteries."They thought that Group 1 monkeys, who received the smallest amount of dietary cholesterol (equivalent to about 86mg cholesterol/day for humans), would not experience adverse effects. They did.
What's an occasional egg? From Spence's earlier paper:
"The effects of dietary cholesterol on serum cholesterol are, in part, dependent on the diet and the characteristics of the individual consuming the cholesterol. Dietary cholesterol has a much greater effect on people consuming a low-cholesterol diet, with a threshold effect as shown by Connor et al. In their 1961 study, Connor et al also showed that egg yolk, containing 240 mg of cholesterol, had a greater hyperlipidemic effect than pure crystalline cholesterol dissolved in oil. In people consuming a low-cholesterol diet, egg yolk intake increased fasting serum cholesterol level by 40 mg/dL."