#472: Compared To What? – Understanding Food Substitution Analysis & Adjustment Models

Sigma Nutrition Radio

Danny Lennon

Nutrition, Health & Fitness

4.8 • 633 Ratings

🗓️ 28 February 2023

⏱️ 53 minutes

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When thinking about the effect of eating or not eating a certain food or nutrient, we can't consider this in isolation. Meaning, we need to evaluate the impact within the context of what such an inclusion/exclusion does to an individual's overall diet pattern.

Thinking about this concept, the phrase "compared to what?" has been colloquially used. And while this is an important idea, there has been some misapplication of this principle.

In nutrition science, this is related to the concept of food or nutrient "substitution". And this concept is crucial to understanding the issues that can arise in nutrition studies, particularly when it comes to single food analyses in nutritional epidemiology.

This concept of substitution is quite intuitive in controlled feeding studies. However, it is not as obvious when considering nutrition epidemiology studies. As noted by Ibsen & Dahm (2022):

"Whereas studying the effects of eating one food instead of another is typically explicit in interventional study designs, it is often implicit and sometimes hidden in analyses of observational studies."

However, in nutrition epidemiology substitution is still happening, but it typically emerges as a consequence of adjustment models. In nutritional epidemiology, it is essential to adjust for confounders. E.g., one vital adjustment is often for total calorie intake. However, when our exposure is a specific food/nutrient, we must think about confounding by other foods.

So knowing what, and how, a study is adjusting for variables helps us interpret it better.

In this episode, Dr. Alan Flanagan and Danny Lennon discuss these crucial ideas of food substitution, adjustment models, and "compared to what?".

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0:00.0	Hello, welcome to Sigma Nutrition Radio. This is episode 472 of the podcast.
0:21.6	My name is Danny Lennon and with me is Dr. Alan Flanagan.
0:25.6	Alan, how are you today, sir?
0:27.6	I'm very well.
0:28.6	I'm very well.
0:29.6	We have, I think, what is going to be quite an interesting topic to explore and certainly
0:34.6	for people who are interested in getting the most they can out of reading
0:38.3	nutrition research or at least understanding sometimes why issues come up in certain types of
0:43.4	studies as we'll discuss but this idea of food substitutions and within that we can also look at
0:49.7	nutrient substitutions we're going to look at some ideas around adjustment models in research.
0:54.8	But really this idea of when we're trying to compare foods or we're doing a food substitution
0:59.9	analysis, what this actually means, what this means for those of us just trying to read research
1:04.7	and understand some of the implications from that. And then as we'll get to importantly,
1:09.0	what this concept isn't or how it can be maybe
1:11.8	misunderstood. So first of all, maybe as a place to get everyone on level footing, when we're
1:20.5	thinking out of this basic concept of substitution, specifically in the context of nutrition
1:26.0	science and nutrition research, what would be a useful
1:30.2	way for people to conceptualize this? What is an easy way for us to maybe first give a simple
1:35.6	explanation of what we're trying to do or what this actually is? So with nutritional epidemiology,
1:42.3	it is, of course, observational research. There is no intervention,
1:47.0	and the diet that is being assessed is being assessed in a population of free-living individuals
1:52.4	who are going about living their life. And this obviously, as an observational design,
	...

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