The two things, i.e. (1) cholesterol concentrations in the blood and (2) the amount of cholesterol consumed through food (dietary cholesterol), were once thought to be directly related, but now it's pretty well established that the relationship between the two is quite weak.
To make it short:
(1) Lower blood cholesterol is good because it lowers the risk of heart attack and ischaemic stroke (the most common type of stroke - caused by artery clogging, like a heart attack).
(2) Lower dietary cholesterol is, currently, sometimes downplayed as being unimportant, but it may very well be at least somewhat important (it looks like it) to lower the risk of cancer (Darooghegi et al. 2022, Miao & Guan 2021, Jin et al. 2019). And maybe cholesterol-rich foods aren't very good for your heart either (Zhao et al. 2022).
Details of the study:
Participants
- Number of participants: 207 (total number) = 59 vegans (VEGAN) + 55 lacto-ovo-vegetarians (LOV) + 93 omnivores (OMN)
- At least 18 years old
- Lacto-ovo-vegetarian or vegan diet for at least 6 months
- Recruited at the university campus [presumably: Institute of Food Science, Technology and Nutrition (ICTAN), Madrid] and vegetarian associations [the authors didn't write which]
- The participants were self-classified in one of the diet groups (omnivore, lacto-ovo-vegetarian or vegan) and the classification was validated [which is good; i.e. they asked if the really did not eat any meat etc.]
- On average, all three diet groups had a healthy body weight (i.e. not "overweight" or "underweight").
- Women represented 62% of the total.
- Ethnicity was >98% Caucasian.
I've changed the authors' abbreviation "VEG" for "vegan" to "VEGAN", to avoid misunderstandings.
Main results
- Systolic blood pressure was lower in LOV and VEGANS [which is good] than in OMN. Especially in men: systolic blood pressure was 7 mmHg lower in VEGAN men than in OMN men.
- Total cholesterol and LDL-cholesterol were lower in the LOV and VEGANS [which is good] than in the OMN.
- Cholesterol intake (dietary cholesterol) was lowest in VEGANS [which is good], lower than in LOV, which was in turn lower than in OMN.
From Figure 2 in Garcia Maldonado et al. (2023):
"Fig. 2 [...] Open bars, men; filled bars, women. Differences between diets: [...] ***p < 0.001."
In this study, vitamin B12 levels or other nutrient levels/markers were not measured - or at least they were not reported in this article (which ideally should be the case). And in they ClinicalTrials.gov registry, I cannot see this info either.
One average, the VEGANS (women: 27 years; men: 29 years) were older than the OMN (women: 25 years; men: 26 years). Because of this age difference, I would have liked to see the results adjusted for age (statistically) - which might have made the advantage of the VEGAN group (lower cholesterol levels) even clearer. But probably this wouldn't have made much of a difference.
Other results
- The prevalence of anaemia (haemoglobin lower than 12.5 g / dL) was 10% independently of diet group.
- There were differences in lymphocyte counts, with LOV and VEGANS presenting lower values than OMN - it's uncertain what this means but could be related to lower levels of inflammation in the LOV and VEGANS.
- Vitamin B12 supplements were used by 81% of VEGANS, 54% of LOV, and 5% of OMN - this leaves us with the question: What did the other 19% of VEGANS do who did not take a B12 supplement?
- Protein supplements were used by less than 10% of the subjects (6% OMN, 9% LOV, and 3% VEGANS), without significant differences between diet groups.
- The use of other supplements such as iron, calcium or vitamin D was much lower (<3%).
Interpretation of the results
The authors write: "[...] consistent with different findings in vegetarians [in other studies], total-chol[esterol] and LDL-chol[esterol] levels were lower in LOV and VEGANS than in OMN and were similar in the two vegetarian groups [...]".
"Results clearly show that there is no parallelism between cholesterol intake [dietary cholesterol] and serum levels [blood cholesterol levels], and that there is a threshold around 150 mg [/] dL [.] that represents endogenous cholesterol production. In fact, VEGANS with negligible cholesterol intake, had similar serum total-chol and LDL-chol than LOV [...]."
"[...] OMN [...] presented serum total-chol below the lower recommended level of 200 mg [/] dL [.].
"[...] we can conclude that all three diet groups had low cardiometabolic risk." This isn't surprising at all because they were young and had a healthy body weight.
Extra info (not from this study):
What, I think, should be mentioned here is the potential importance of this small advantage of VEGANS and LOV of having lower cholesterol levels at a young age - if these people stay with their animal-flesh-free dietary patterns:
Brian Ference on the importance of LDL cholesterol lowering:
I'll quote Brian Ference, a renowned cardiovascular expert ("a cardiologist and genetic epidemiologist who was educated and trained at Yale, Harvard, Oxford and Cambridge Universities"):
"[...] LDL [cholesterol] is not merely another risk factor. Instead it is the main cause of atherosclerotic cardiovascular disease. [...]
And that presents us with an opportunity to intervene early, to dramatically reduce the trajectory of atherosclerosis in low- and middle-income countries and around the world. And indeed there are compelling data to suggest that modest, sustained reductions in LDL can dramatically reduce the lifetime risk of cardiovascular events by 80%, cardiovascular mortality by 2/3, and all-cause mortality by 30%."
"[...] And importantly, what these algorithms suggest is that there is a clear stepwise greater proportional reduction of the risk of cardiovascular events for the same unit reduction in LDL with each decade earlier we start. But perhaps more importantly they suggest that modest sustained reductions, beginning earlier in middle life, are much more effective at reducing the risk of cardiovascular events than the current strategy of much more aggressive LDL lowering late in life, really providing the opportunity to make profound reductions in the burden of atherosclerotic cardiovascular disease around the world."
"[...] the prevention paradox suggests that we lower LDL and blood pressure just a little bit, to shift the curves, [with which] we can reduce [the total number of cardiovascular] events enormously, which is what the experience of Finland in the 70s and 80s [was]. By contrast, the other approach is to just focus on those high-risk patients and treat them aggressively, which turns out, because there are fewer people at high risk, we prevent fewer events. [...] We have to sort of promote health policies and societal policies that reduce mean LDL and blood pressure to give us a head start and then to slowly integrate these digital technologies that can bespokely attend to each person's individual trajectory to identify not who needs necessarily aggressive treatment but to titrate each person's individual reduction in LDL and the other modifiable causes of irreversible accumulated injury to the artery wall slowly over time in order to most efficiently allocate resource. [...]"
(This quote is from a speech he gave at the European Atherosclerosis Society conference in Milan, in May 2022. I have an audio recording of these segments.)
P.S.: Not all vegans have great cholesterol levels. If you're vegan and your cholesterol is high, click here.