Although there are undoubtedly persons who would choose to participate in a lifelong regimen of dietary change to achieve results of this magnitude, we suspect that some might not.
William Taylor et al., “Cholesterol Reduction and Life Expectancy,” 1987
When I think about preventive medicine and the efforts we might take to extend our lives, or at least our healthspans as the longevity gurus like to put it, the first question that comes to mind is: is it worth it?
To know if it’s worth it, of course, we need some idea of the expected benefits. How much longer can we expect to live, or at least stay healthy, if we do what’s proposed, if we take the pill, eat the diet, engage in the exercise program... pick your panacea? Once we know that, we can weigh those expected benefits against the risks, costs, and effort required, and do the risk-benefit analysis needed to make an informed decision.
Hence, today’s quiz of the day, on the very touchy subject of LDL cholesterol, specifically the benefits of eating a cholesterol-lowering diet.
Here’s the caveat, though: we’re assuming that the conventional wisdom is right about the dangers of LDL cholesterol and that we’d all benefit from keeping it low. Unlike many of my posts, we’re going to assume the American Heart Association has always been right about this and we should have been taking their advice all along. Researchers I respect will tell me they’re not, and I have argued otherwise in my books, but for this post let’s assume they are.
So… If you were to avoid saturated fat from this moment onward—faithfully replacing the obvious sources (butter! fatty meats!) with unsaturated fats instead (assuming, also for the sake of argument, that those are all benign)—and you lowered your LDL cholesterol below 100 mg/dL, as the American Heart Association recommends, how much longer could you expect to live? This is a multiple-choice question:
1. Days longer than otherwise?
2. Months longer?
3. Years longer?
4. Decades? (Instead of having a fatal or crippling heart attack or stroke in your 50s or 60s, you avoid it and get to see your grandchildren graduate from college.)
5. Nobody has any idea.
Since you might need some guidance, here’s what the most recent Cochrane Collaboration systematic review (2020) of the relevant clinical trials says about the benefits of lowering LDL cholesterol with a “modified-fat” diet.1 Whether this will help answer the quiz-of-the-day question is unlikely, but it’s the best we’ve got:
The included long‐term trials suggested that reducing dietary saturated fat reduced the risk of combined cardiovascular [heart attack, angina, stroke] events by 17%...
We found little or no effect of reducing saturated fat on all‐cause mortality... or cardiovascular mortality... [or] on non‐fatal myocardial infarction... or CHD mortality... Effects on total (fatal or non‐fatal) myocardial infarction, stroke and CHD events (fatal or non‐fatal) were all unclear as the evidence was of very low quality. There was little or no effect on cancer mortality, cancer diagnoses, diabetes diagnosis, HDL cholesterol, serum triglycerides or blood pressure, and small reductions in weight, serum total cholesterol, LDL cholesterol and BMI. There was no evidence of harmful effects of reducing saturated fat intakes.
The trials in that Cochrane review were also biased in a way that would never be tolerated in a drug trial. As the authors point out (in what amounts to the fine print in the reviews, ignored in the abstract and summary), 15 of the 16 trials were unblinded, and 11 or 12 of 16 lacked a control diet, resulting in a bias known technically as “systematic difference in care.” Lacking a control diet is like omitting the placebo in a randomized, placebo-controlled diet. (The results in the trials that did include a control diet were not a reason to be optimistic that avoiding saturated fat is a good thing.)
Those biases are good reasons to question even that 17% number. But let’s assume this is real, an effect of the diet, not of the biases built into the trials. So how much longer could you expect to live had you swapped out the saturated fat in your diet for unsaturated fat, lowered your LDL cholesterol by, say, 20% or even 30%, gotten it safely under 100 mg/dl, and stuck to your “heart-healthy” diet for the duration?
Okay, this was a trick question. Five is the correct answer, for multiple reasons—nobody has any idea--though if you chose 1 or 2 (days to weeks), you’d have been on safe ground.
The answer depends partly on your baseline risk of heart attack—the higher your risk going in, the greater the benefit—but mostly on how we interpret the statistics from clinical trials and observational epidemiology. And here’s where “nobody has any idea” means, literally, nobody has any idea.
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