Many variables
This is because there are an awful lot of variables that all interact within the larger lifestyle topics such as nutrition, training, stress and mental which makes unravelling this tangle incredibly difficult. If this is not complex enough, you also run into the problem that every person is different, so health advice is ultimately bespoke.
This, while scientists like to show that certain associations apply to large groups of people. Then those links should also preferably be proven causal (causal) rather than just an association under which all sorts of causality confusions can lie.
Cases are simplified first
These blood values often don't say everything either. For example, you can measure in blood that LDL cholesterol rises when you eat a lot of saturated fats, which does not distinguish between saturated fat sources so that a Double Whopper or a smoothie with coconut fat are lumped together.
LDL- cholesterol is known as a blood marker of cardiovascular disease, a predictive value therefore, because in many people who develop cardiovascular disease, LDL cholesterol is elevated. Thereby, LDL cholesterol is only 1 blood marker for cardiovascular disease while there are many more such as HbA1C, triglycerides, Apo-B, hsCRP and homo cysteine.
Helicopter view / holistic view
I therefore do not believe in flattening the scientific discussion into oversimplifications. It is not about individual substances in food, but about contexts in which those substances interact. It is not about blindly focusing on 1 blood marker, but about looking at many processes at once that interact with each other in the context of a unique human being.
Holism versus reductionism
When I was studying at Wageningen University, I noticed that reductionism was the leading paradigm. And this only got worse the more the food industry got a finger in the pie there.
Biochemists and substance thinkers
In my opinion, medics have also interfered too much in the discussion of diet and lifestyle in relation to health. Equine remedies, as medicines often are, easily provide a proven effect compared to a placebo.
Separate nutrition and lifestyle intervention points rarely lead to such evidence.
And the fact that the Mediterranean diet is known as the most scientifically supported healthy way to live is really not because of a bit more olive oil or a glass of wine a day. These people are probably doing all kinds of things right in several lifestyle pillars such as not eating too much, traditionally eating less processed food, eating with attention, having nurturing contacts, being outside more in sunny surroundings, having meaning, having less chronic stress and much more.
Tunnel vision
I am not a fan of thinking too reductionist, because there is a high chance that you will have chosen the wrong focus anyway and that you will create tunnel vision with accompanying huge blind spots.
Yet I feel that this still puts me in a minority as a scientist and that reductionist scientific thinking still reigns supreme in the discussion of health, nutrition and lifestyle.
As a holistic thinker, you are quickly pigeonholed as alternative, unscientific, guru or quackery stopped. And this while I believe that holistic science will eventually win out and help modern 'ai' short-sighted scientists to be able to transcend their limited reductionist assumptions. And that is just as well!