Have you ever seen the latest documentary on Netflix known as “You Are What You Eat: A Twin Experiment?” The documentary appears at how totally different diets have an effect on units of twins’ well being.
The present concluded {that a} plant-based (vegan) food regimen is more healthy than an omnivorous food regimen. Whereas which will (or might not) be true, we are able to’t verify that from this research. Why? Many scientists have recognized shortcomings within the design of their research. Scroll right down to determine for your self!
Research Design: Barbie Dolls and The Impartial Variable
Let’s run by a fast thought experiment earlier than we soar into the documentary.
Think about that your daughter’s birthday is arising, and also you’re making an attempt to find out which kind of Barbie doll she prefers to play with. You hypothesize that she likes blonde Barbies over brunette Barbies. To search out out, you permit her to play with two teams of Barbie dolls – one group being blonde, the opposite being brunette – to see which group she performs with for the longest. Every of the Barbie dolls is sporting a singular outfit from the opposite Barbies. A lot of the blondes are sporting pink and a lot of the brunettes are sporting blue.
You discover that your daughter performs with the blonde Barbie dolls considerably greater than she performs with the brunette Barbie dolls. So, you assume that she likes blonde Barbies greater than brunette Barbies – proper? Not essentially!
Why? For the reason that blondes have been sometimes sporting pink and the brunettes have been sometimes sporting blue, you couldn’t know for positive whether or not your daughter loved taking part in with the blonde Barbies as a result of they have been sporting pink or due to the colour of their hair.
How would you recognize for positive that your daughter prefers blonde-haired Barbie dolls? You’d have needed to make the Barbies equivalent to one another except for their hair coloration. AKA, you must have put all the dolls in equivalent outfits in order that hair coloration is the one distinction examined in your experiment. In science, we name this (the one element that’s modified) an “unbiased variable.”
Let’s check out the research design within the Netflix documentary and determine whether or not it included an unbiased variable.
Their Research Design vs. Our Barbie Doll Research Design
The producers of the present designed the research. Their goal was to learn how adhering to particular diets – particularly, a wholesome vegan food regimen and a wholesome omnivorous food regimen – would have an effect on the metabolic and cardiovascular well being of their individuals.
In an try to manage for genetic variations within the diets’ results, the producers used twins of their research. Over eight weeks, one twin would eat the vegan food regimen and the opposite twin would eat the omnivorous food regimen. A number of units of twins have been enrolled. Their metabolic and cardiovascular well being markers have been examined earlier than and after the food regimen interval.
The individuals who adopted the vegan food regimen noticed extra vital enhancements in LDL-C than the omnivorous group. LDL-C is a vital cardiovascular well being marker – having unhealthy ranges is related to coronary heart assault threat, amongst different issues.
So, it sounds just like the vegan food regimen was more healthy than the omnivorous food regimen, proper? Not so quick! Let’s examine to verify there may be an unbiased variable.
First – props to the producers for utilizing twins. This controls for genetic variations between research individuals.
However is the food regimen the one factor that was modified between the teams? Not fairly.
The place the Documentary Falls Quick: No Impartial Variable
Right here’s the place issues get precarious. The individuals following the vegan food regimen consumed fewer saturated fat and fewer energy than the individuals following the omnivorous food regimen.
Suppose again to our Barbie doll thought experiment. How may we inform if our daughter most popular blonde Barbies if every group of Barbies wore totally different outfits? Possibly the outfits performed a task in her doll choice. Equally, within the documentary, how can we inform it was veganism itself that made the distinction within the individuals’ LDL-C ranges? Possibly it was the decrease energy and saturated fat that affected the change.
Ideally, the producers would have managed for energy and saturated fat – that means they might have made each twins eat the identical quantity of energy and saturated fat. That method, we may see whether or not it was veganism itself that created the advantageous outcomes.
Does this imply the documentary’s findings are ineffective? Not utterly! We do see that individuals who eat vegan diets sometimes eat fewer energy and saturated fat than those that eat omnivorous diets. Nevertheless, the important thing phrase is sometimes – not “all the time.” Simply understand that you could possibly get the identical impact whereas consuming an omnivorous food regimen by reducing energy and saturated fat. We simply don’t know for positive.
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