“Study proves that drinking green tea reduces weight by 25%!”. But, before you down tools and rush off to stock up on green tea, do you ever try to read behind the headlines? Do you ever take a long, hard look at the original study paper?
I love good nutrition science – I even have the T-shirt (!) It plays a key role in directing public health nutrition policy and in helping set clear guidelines for improving the health of the population. What I hate is bad nutrition science which has me rolling my eyes to the heavens and muttering (very) rude words under my breath. Bad nutrition science misreports or exaggerates nutrition research results, and there is a real risk that following “bad nutrition science” advice could adversely affect people’s health.
A little background about nutrition research. In an ideal world, you want to be reviewing the impact of a particular aspect of nutrition on a large group of people, not animals (which is known as in vivo) or cells (known as in vitro), simply because animals and cells might just possibly not react in the same way as people (!)
Logically, to test whether something works or not, you’d want to compare two groups, one group (known as ‘the experimental group’) would change one aspect of their diet while the other group would continue as normal (known as the ‘control group’). You’d then compare the results after a period of time to see if the dietary change had produced the anticipated effect (or not!).
Note that: people should be randomly allocated people to the two groups, rather than cherry picking which group they belonged to. For example, it’s well known in weight loss studies that people who weigh more tend to lose weight more quickly on an initial diet. So, allocating these people to the experimental group during a weight loss trial could distort the results.
These types of studies are known as randomised controlled studies, and are the ‘gold standard’ for setting nutrition policy as, if performed correctly, they prove whether a particular nutrition approach works.
The downside? These are very expensive to perform and difficult to conduct. Most nutrition studies tend to be observational, where a large group of people are observed for a period of time but you can’t conclusively prove whether a particular nutrition strategy works. For example, an observational study might find that people who eat dairy products have better bone health, but you can’t conclusively prove from this study that eating dairy improves bone health. People who eat dairy might exercise more or eat more green vegetables, both of which are also good for bone health.
Crystal clear?! Other useful insider tips when looking at nutrition headlines include looking at how the data is collected and how the results are measured. A well-known fact is that most participants tend to ‘understate’ the amount of food they eat by about 20%, so food diaries and food questionnaires might therefore not be 100% accurate. And, never ever forget to see if there any conflicts of interest on the researchers performing the study.
So, are you ready to put it all together?! Let’s go back to our original headline:
“Study proves that drinking green tea reduces weight by 25%!”
And, like good nutrition scientists, we go back to the original nutrition paper.
This study was performed on four mice for a period of two weeks, with the mice being given green tea to drink instead of water. The mice were weighed on a scale at the beginning and end of the two-week study period. Professor X is an executive director of “I Love Green Tea”.
So, like Sherlock Holmes, what do we deduce?
- This study is seriously dodgy
- Mice are not people, people!
- The sample size and the study intervention time period are both completely inadequate
- Suspicious thoughts (!): How were these mice chosen, were they overweight to begin with? Were there any dietary changes in addition to the green tea?
- No control group, so unable to compare the results
- A simple weighing scale cannot show fat loss.
- Massive conflict of interest!!!!
As for green tea, yes, there are studies to show that it is good for us. It’s full of antioxidants which help to support our health, it’s a great source of L-theanine, an amino acid which promotes concentration. As for fat burning though? The evidence is about as clear as mud, with some small trials, finding a slight benefit, while other larger trials show no benefit.
So are you still going to go rushing out to stock up on green tea for ‘rapid fat loss’ now we’ve reviewed the original research? Possibly not. This is why you need to be able to spot bad nutrition science!