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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?”.
Dr. Alan Flanagan has a PhD in nutrition from the University of Surrey, where his doctoral research focused on circadian rhythms, feeding, and chrononutrition.
This work was based on human intervention trials. He also has a Masters in Nutritional Medicine from the same institution.
Dr. Flanagan is a regular co-host of Sigma Nutrition Radio. He also produces written content for Sigma Nutrition, as part of his role as Research Communication Officer.
Danny Lennon has a master’s degree (MSc.) in Nutritional Sciences from University College Cork, and he is the founder of Sigma Nutrition.
Danny is currently a member of the Advisory Board of the Sports Nutrition Association, the global regulatory body responsible for the standardisation of best practice in the sports nutrition profession.
- Principle of subsititution analysis in nutrition science
- Confounders and adjustment models
- Nutrient subsitution
- Food substitution
- “Compared to what?” – what it means and what it doesn’t
- Why knowing what, and how, a study is adjusting for variables helps us interpret it better.
- Recommended Reading:
- Tobais et al., 2022 – What Eggsactly Are We Asking Here? Unscrambling the Epidemiology of Eggs, Cholesterol, and Mortality
- Ibsen et al., 2021 – Food substitution models for nutritional epidemiology
- Ibsen & Dahm, 2022 – Food substitutions revisited
- Song & Giovannucci, 2018 – Substitution analysis in nutritional epidemiology: proceed with caution
- Tomova et al., 2022 – Theory and performance of substitution models for estimating relative causal effects in nutritional epidemiology
- Willet et al., 1997 – Adjustment for total energy intake in epidemiologic studies
- Referenced in this episode:
- Related Podcast Episodes:
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