Large double-blind, controlled studies with human subjects, over long periods of time tend to be very expensive, and difficult to pull off. Thus, there always is some trade-off. But IMO it's irresponsible to ignore smaller studies if a trend between them is established, which is usually the object of a meta-analysis, to find trends in acquired data.
I think what he is trying to say is most people don't recognize their limitations. If you don't have an advanced degree (Wikipedia PhD's don't count) or extensive education in a scientific field, evaluating a body of scientific literature is probably not going to be one of your strong suits. This is not necessarily a problem, as long as you realize this and act accordingly.
The problems arise when people fail to recognize weaknesses. The inherent weakness of a rubber band isn't a problem unless you fail to realize it and try to bungee jump with one. Liekwise, a lack of expertise in a field is only a problem if you don't realize it. I've seen people with great expertise in one area completely embarrass themselves (without even realizing it) by thinking their skills in X somehow gave them an ability to understand science.
I'm sure you are probably more familiar with many concepts than the average person. But this greater level of knowledge may have led you to believe you have a comprehensive understanding of the subject, and this, in due order, has led to believing you know more than the majority of the scientific community.
I must admit, it is rather difficult for me to understand, to imagine that I am an expert in a subject in which I have little or no training. Even as a phd candidate and doctor in training, I wouldn't ever claim to know more. What's odd is this type of behavior doesn't seem to happen much outside the sciences. You don't hear of people thinking they have expertise in building houses or car repair. It might be because when people try to play an expert in these areas, they run up against the sharp tip of reality more often.
Take home message: If you're not a professional--meaning you're not paid for your research and don't have a bunch of fancy letters after your name--acknowledge this fact and don't pretend you are. Consensus is your best bet.
Yeah. It seems backasswards to include in the meta-analysis the studies with larger subjects and more compromised methodology. Wouldn't it make more sense to compile all the most controlled studies where the variables are known or more precise regardless of sample size?
Effects of Saturated Fat on Plasma Lipids and Lipoproteins
In humans, saturated fat intake increases LDL cholesterol in comparison with all nutrients except trans fats [2
High Carbohydrate Intake Contributes to Dyslipidemia
Elevated triglycerides, reduced HDL cholesterol concentrations, and increased concentrations of small, dense LDL particles characterize the dyslipidemia that is part of a metabolic profile considered to be a major contributor to increased CVD risk. Both insulin resistance and high carbohydrate intakes have been shown to contribute to this dyslipidemia, and refined carbohydrates, in particular, can raise triglyceride and lower HDL cholesterol concentrations [23]. Of interest, reductions in dietary carbohydrate, even in the context of a diet high in saturated fat, have been associated with reduced concentrations of small, dense LDL [5].
The type of carbohydrate consumed can affect blood lipid profiles. Using the glycemic index (GI) as a classification system that rates dietary carbohydrates by their ability to increase postprandial blood glucose levels, the consumption of lower-GI foods has been associated with lower triglycerides and higher HDL cholesterol [24]. Substituting low-GI foods for high-GI foods may lower triglyceride concentrations by 15% to 25% [25]. There is also considerable evidence that high intake of added sugars [26], and fructose in particular [27], adversely affects all components of atherogenic dyslipidemia. Most recently, an evaluation of data from 6113 adults participating in the National Health and Nutrition Examination Survey (NHANES) showed a positive correlation between added sugars and dyslipidemia [28]; the minimization of sugars as a component of the American diet would be expected to improve these diet-induced abnormal lipid profiles.
Effects of Saturated Fat on Coronary Heart Disease
Animal Studies
Assessment of the effects of dietary saturated fat on atherosclerosis has been studied in various animal models [9
Observational and Prospective Epidemiologic Studies
Although early epidemiologic studies linking saturated fat with blood cholesterol and blood cholesterol with CHD were important in defining a conceptual model of etiology for CVD [33, 34], they were a simplification of the complex relationship of nutrients to disease outcomes. These studies were based on aggregated data and did not adjust for potential confounders (eg, trans fatty acids, polyunsaturated fatty acids, and high-GI carbohydrates), some of which have only more recently come to be known as relevant in modulating CVD risk.
Prospective cohort studies are designed to enable the evaluation of potential baseline disease determinants with future disease outcomes by following a cohort of study participants over a period of time. Large, prospective epidemiologic studies have the advantage of being able to adjust for co-variates, so that the effects of a specific nutrient can be assessed. However, caveats to such studies include the reliance on nutritional assessment methods with varying accuracy and the assumption that diets remain similar over the long term.
Our recent meta-analysis summarized data related to saturated fat and CVD from 21 prospective epidemiologic studies that included 347,747 men and women [35
Of note, some studies have suggested that saturated fat may increase LDL cholesterol only if the polyunsaturated fat intake falls below a threshold level; specifically, the availability of linoleic acid may determine the cholesterolemic effects of other fatty acids [16]
This second scenario clearly refutes the original lipid hypothesis that posited that saturated fats caused CHD.
I think what he is trying to say is most people don't recognize their limitations. If you don't have an advanced degree (Wikipedia PhD's don't count) or extensive education in a scientific field, evaluating a body of scientific literature is probably not going to be one of your strong suits. This is not necessarily a problem, as long as you realize this and act accordingly.
The problems arise when people fail to recognize weaknesses. The inherent weakness of a rubber band isn't a problem unless you fail to realize it and try to bungee jump with one. Liekwise, a lack of expertise in a field is only a problem if you don't realize it. I've seen people with great expertise in one area completely embarrass themselves (without even realizing it) by thinking their skills in X somehow gave them an ability to understand science.
I'm sure you are probably more familiar with many concepts than the average person. But this greater level of knowledge may have led you to believe you have a comprehensive understanding of the subject, and this, in due order, has led to believing you know more than the majority of the scientific community.
I must admit, it is rather difficult for me to understand, to imagine that I am an expert in a subject in which I have little or no training. Even as a phd candidate and doctor in training, I wouldn't ever claim to know more. What's odd is this type of behavior doesn't seem to happen much outside the sciences. You don't hear of people thinking they have expertise in building houses or car repair. It might be because when people try to play an expert in these areas, they run up against the sharp tip of reality more often.
Take home message: If you're not a professional--meaning you're not paid for your research and don't have a bunch of fancy letters after your name--acknowledge this fact and don't pretend you are. Consensus is your best bet.
Given the fact that replacing saturated fats for carbs will have zero of a positive effect, it seems fairly certain that "saturated fats cause CVD" cannot be anywhere near an accurate description here. We obviously don't have a complete understanding of it, but it seems quite possible that there is a dynamic interplay of many different factors, with saturated fats, polyunsaturated fats, dietary cholesterol, and maybe down to specific fatty acids, somehow interrelating at once.
Excellent post, excellent advice, and I am sure very few people are going to agree with you sentiments. Your post has the unfortunate quality of offering a reasonable and rational coarse of action.
This is the internet age, however, and people generally tend to believe that they can gather enough information in their spare time and posses a sufficient degree of understanding that their conclusions are more valid than those of the general scientific community.
Of course, the connection was an important first inquiry. It's unfortunate that government stepped in and diet guidelines were set so hastily and that the idea has persisted so stubbornly. Less time and resources would've been spent trying to defend it which could've been spent trying to refine it and flesh it out more (as it seems that we are doing now many decades later).
As with any complex system where multiple variables (both known and unknown) interact, anything so simplistic as the original formulation of the lipid hypothesis just seems intuitively wrong.
Of course, the connection was an important first inquiry. It's unfortunate that government stepped in and diet guidelines were set so hastily and that the idea has persisted so stubbornly. Less time and resources would've been spent trying to defend it which could've been spent trying to refine it and flesh it out more (as it seems that we are doing now many decades later).
Thanks for providing all those studies and rescuing this thread. This conversation was falling into the vague realm of scientific methodology versus sociological phenomena and less about the thread topic.
This must be some weird bizarro world you guys live in where you derive a sense of intellectual superiority by consciously making the choice to be ignorant and letting others do the thinking for you. Congrats on turning a negative into a positive I suppose.
Listening to those who know much more than you is not being ignorant. The surest sign of ignorance is those who act like they know everything.
I agree.
Let me sum a few of my thoughts here:
a) saturated fat/dietary cholesterol does not appear to be the root of all evil
b) replacing saturated fats with carbs appears to be an ineffective strategy for CV health purposes
c) replacing all fats in general with carbs (a la low-fat/high-carb) is definitely ineffective and possibly detrimental for CV health purposes
d) saturated fat/dietary cholesterol not being the root of all evil doesn't mean they can have no detrimental effects on CV health depending on the rest of the circumstances. It seems that, at this point, they may not be warranted a completely blank check.