Publications (newspapers, magazines, and the like) make the bulk of their revenue from advertising. For advertisers to pay premium fees for exposure, journalists work hard in writing headlines that are catchy enough for people to buy the publication/subscription or click on them, depending on the format. That’s the main reason why you shouldn’t get your information from news headlines, or in other words, believe everything you read.
I’ve chosen a recent piece of scientific literature that has had a significant impact in the past week or so. The full-text paper is available online (see references) and is entitled “Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis.”. In a cohort study, researchers measure the extent of exposure of the subjects to whatever is being studied (in this case, carbohydrate) and the outcome is measured later. Cohort studies are NHMRC (National Health and Medical Research Council) level III-2 when rating quality of evidence (levels I is the best level of evidence), so no great for establishing clear causality but may give an indication that something is going on. Meta-analysis means that the researchers compared their study with similar studies to determine if their results were congruent.
The problem with news headlines
My main issue with news headlines is that most of them do not do a good job at communicating what the scientists reported. In this particular case…
Here’s how the authors reported their findings:
“low carbohydrate (<40% of energy from carbohydrate) and high carbohydrate (>70% of energy from carbohydrate) consumption were associated with increased mortality risk and shorter residual lifespan, with minimum risk observed with 50–55% of energy from carbohydrate.” (1)
Here’s how the media reported the article:
“A Low-Carb Diet Could Cut 4 Years Off Your Life, So Just Eat the Damn Pasta” (Esquire)
“Eat PASTA to live longer! Cutting carbs ‘increases risk of early death’, experts warn” (New York Post)
“More potatoes may be healthy after all” (The Times)
In contrast, the following (less sexy) news headlines, do summarise what the research concluded:
“Eating carbs in moderation lowers your risk of early death” (Daily Mail)
“Low and high carb diets increase risk of early death, study finds” (fox5sandiego.com)
“‘Right’ Amount of Carbs May Help You Live Longer” (WebMD)
See the difference? It looks like moderation does not only works for carbs but also for good journalism!
I went ahead and collected 124 news headlines reporting the aforementioned article. Turns out that 57.3% only mentioned the low-carb side of the findings, while 41.1% either mentioned that both low- and high-carb were associated with the increased mortality or that a moderate intake was associated with decreased mortality.
12.9% of headlines mentioned better health as opposed to all-cause mortality as the outcome, which is inaccurate. To illustrate this point, one could live a healthy life and die at 25 in a car crash. 4.8% of the headlines used the word “paleo” or “keto” and 2.4% used the word “pasta”
Other examples of misleading headlines are:
“Carbs aren’t the enemy! Eating carbohydrates can EXTEND your lifespan, study reveals” (Mirror Online). This makes it sound as if carbohydrate intake could add years to one’s life expectancy, which is certainly not what the researchers concluded.
“Harvard study reveals healthiest way to consume carbohydrates” (Deccan Chronicle). No, they did not talk about health outcomes related to carbohydrate consumption, type of carbohydrate, time of consumption, glycemic index, etc.
“Carbs are good for you, Harvard study finds” (The New Zealand Herald). No, they didn’t find that.
In the cohort analysed by the scientists, “a percentage of 50–55% energy from carbohydrate was associated with the lowest risk of mortality. In the meta-analysis of all cohorts (432 179 participants), both low carbohydrate consumption (<40%) and high carbohydrate consumption (>70%) conferred greater mortality risk than did moderate intake… mortality increased when carbohydrates were exchanged for animal-derived fat or protein… and mortality decreased when the substitutions were plant-based.
Figure 3: U-shaped association between percentage of energy from carbohydrate and all-cause mortality in
the ARIC and PURE cohort studies (1)
The main limitation of this study is the way carbohydrate intake was assessed. The cohort analysed in this study were 15 428 middle-aged participants (45-64 years old) from the US. Their dietary intake was assessed by food frequency questionnaires (FFQ) at baseline (i.e. during the initial visit, between 1987 and 1989) and 6 years later. FFQs are not very reliable because they don’t produce reliable estimates of intake quantity, depend on the respondent’s memory and questionnaire design (there is often lack of detail about foods, limited food list, limited portion sizes). In addition, people tend to under-report when answering to FFQs.
In other words, participants completed a FFQ at baseline (with error margin #1) and then another FFQ at 6 years (with error margin #2, presumably higher because they were 6 years older). From year 6 to 25, the carbohydrate intake was assumed to be the mean of the 2 measurements (!) except for subjects who developed heart disease, diabetes or stroke before year 6, in which case baseline was considered constant (!!).
I won’t continue writing about issues with the actual paper because my point was to critique the news headlines, not the article per se. There are a few good analyses out there highlighting its flaws.
By now it should be clear that you shouldn’t draw conclusions from news headlines, even from reputable sources. The catchiest headlines are often the most misleading. If you have access to the original paper, go ahead and read it. If you don’t know how to read a scientific article, see the links below:
- The Non-Scientist’s Guide to Reading and Understanding a Scientific Paper (Elysium Health)
- How to read articles about health (Dr Alicia White)
- How to Read and Understand a Scientific Paper: A Step-by-Step Guide for Non-Scientists (Jennifer Raff)
Regarding the whole carbohydrate conundrum, I hope it’s clear that science has not determined that eating more carbs “is healthier” or “extends your life” full stop. Quality of food, type of carbohydrate and individual tolerance are important factors to keep in mind.