by Alejandra "Alex" Ruani — Get free science updates here.
“Here we go again”, I thought, rolling my eyes. Why, you may wonder…
In the past days, I noticed major media outlets flooded with 2 incendiary headlines.
Each headline boasted opposite results about saturated fat intake. How come?
- One headline stated: “Saturated fat could be GOOD for you, study suggests”
- But the opposing one said: “Just a small cut in saturated fats reduces heart disease RISK”
Poles apart… So, which one is it?
Imagine the confusion this causes in consumers’ minds.
One headline says “good for you”. Whereas the other one hints “bad for you, cut it to reduce health risk”. All within days!
So I went in, and inspected both rival scientific studies. I’ll walk you through my validation process. The same process we scientists use at The Health Sciences Academy.
Hopefully this exercise will help you discern fact from fiction when it comes to this heated debate.
New to the ‘sat fat’ debate? In short, there’s ongoing controversy about how much of a ‘threat’ saturated fat poses to your health. Saturated fat is abundant in animal food products such as butter, cheese, and meat, as well as some plant-based foods such as coconut oil, nuts, and avocados. Example below:
Inspecting Study No. 1
I’ll begin with the study behind the “good for you” headline. What does it tell us?
The first thing I discovered when analysing it is that the shock headline misreported the study findings and its context.
The study is okay, but the reporting is bad.
And that’s how junk science often spreads around the web. When the research isn’t properly interpreted by media and bloggers.
Let’s look at some of the key inconsistencies, so you can spot bits like these the next time you see conflicting news stories!
As I was reading the first study, I could tell that the researchers mainly looked at fat loss and insulin levels, but not “overall good health” per se.
Question to ask yourself: Is there a mismatch between the news headline and the study objective? Yes, here we have a mismatch. Bad sign.
2. Variables and context
I was curious to see what the participants ate. The researchers assigned them to two different diets:
- a higher-fat, lower-carb diet (73% of calories from fat, 10% from carbs) or
- a higher-carb, lower-fat diet (30% of calories from fat, 53% from carbs).
Both diets emphasised low-glycaemic carbohydrates and minimally processed foods.
No hydrogenated or trans fats, no added sugars, no highly processed foods. All excluded.
Question to ask yourself: What’s the context (or diet) in which the findings emerged? Here, saturated fat was consumed during carbohydrate restriction. Meaning we cannot say “good for you” if the high-fat intake is simultaneous to high-sugar intake, for instance. So no, sugary shortbread cakes haven’t been ‘okayed’!
Both diets resulted in similar fat loss and similar reductions in body weight. One wasn’t “better” than the other.
Question to ask yourself: What are the actual study results? In this case, similar results from both diets. No “winner”.
4. Length and participants
The study was very short (12 weeks) and only involved 38 middle-aged Nordic men with abdominal obesity. This doesn’t represent “everyone” or “you” – as the headline wrongly suggests. We can’t extrapolate these outcomes to everybody else.
Questions to ask yourself: Was it a short- or a long-term study? Who were the study subjects? Was it a small or a large group? When the study is short and the group is small, there’s also a higher risk of a “false positive” (translation: a one-hit-wonder that cannot be reproduced in an identical experiment). Replicability is the secret sauce of good science (see number 6 here).
5. Ethnic and geographical differences
Unlike other humans, cold-climate Arctic and Nordic populations are known to be genetically well-adapted to tolerate huge amounts of fat (example here).
Question to ask yourself: What’s the ethnicity of the study subjects? The subjects were Norwegian. This means we cannot conclude the same for other populations (e.g. Asians) who evolved on different climates, different foods, and experienced different nutrient adaptations.
6. Nutritional genetics
Genetic testing was not included in the research. I’m not sure someone with the “high-carb gene” would have done as well eating 73% in fat calories! The high-carb gene was discovered recently and, if you’ve been paying attention, I introduced it to you in my previous Science Catch-up.
Conversely, there are several genes associated with inefficient fat metabolism. So if you cannot metabolise saturated fat or ketone bodies properly, a high fat diet can do more harm than good. We investigate those and other 21 nutrient-related genes in this Science Report (optional resource).
Question to ask yourself: Did the study investigate the participants’ genetic variants? Some of the best-quality studies I’ve seen take into account inter-individual variability, and looking at the participants’ key genetic variants helps narrow this down. This is the direction of new science. Quite honestly, the rest is getting outdated given how fast personalised nutrition research is moving.
Limitations are like the “small print” – disclaimers for dubious components in a study which need to be taken with a pinch of salt.
We already discussed some limitations earlier on, like a small number of participants, no long-term assessment, and a higher risk of false positives.
Question to ask yourself: What are the study limitations? In this one, there wasn’t a “control group” either – such as people consuming their regular diet. A control would have allowed us to rule out alternative explanations of the results. For all we know, the low-glycaemic eating or the removal of trans fats could have also caused the fat loss and insulin sensitivity improvement.
With headline number 1 debunked, shall we dive into headline number 2?
Inspecting Study No. 2
The debate about the risks of saturated fat continues.
The current UK guidelines on saturated fat indicate:
- no more than 30 grams a day for men and
- no more than 20 grams a day for women.
But many criticise these guidelines, arguing that there isn’t a proven link between sat fat consumption and heart risk, and that there’s no point in limiting its intake.
This new observational study from Harvard and Unilever suggests the opposite: that there is a link between saturated fat intake and heart disease risk. Well, is there?
Key ‘filter’ questions
Let’s use the same questions we asked in the first study to dissect this news story:
Is there a mismatch between the news headline and the study objective? No, we have a match. Remember, a match is what we want.
What’s the context (or diet) in which the findings emerged? Varied diets, at free will. Participants reported what they ate for about 24-28 years.
What are the actual study results? Replacing just 1% of calories from saturated fat by polyunsaturated fats (e.g. Omega 3), monounsaturated fats (e.g. Omega 9), wholegrains (e.g. oats, brown rice) or plant proteins (e.g. pulses), led to a 5% to 12% lower risk of heart disease.
4. Length and participants.
Was it a short- or a long-term study? Who were the study subjects? Was it a small or a large group? A long-term study, with a large group of 73,147 female nurses and 42,635 male nurses. All of them were healthy at the start of the study. They completed lengthy food and health questionnaires every 2 or 4 years for 24-28 years.
5. Ethnic differences.
What’s the ethnicity of the study subjects? Very mixed. White, African American, Asian, and others. But the analysis doesn’t include the relative intake risk per ethnic group.
6. Nutritional genetics.
Did the study investigate the participants’ genetic variants? No, this technology didn’t exist when they started. So it makes it very difficult to understand inter-individual variability, and general findings may not apply to “everyone”.
What are the study limitations? Because it’s an observational study, the self-reporting by the nurses could introduce inaccuracies. Also, those who ate more sat fat were more likely to engage in less physical activity, less likely to take multivitamins, and had a higher caloric intake. Meaning that these factors (called “confounders”) could have increased heart disease risk too, and not just the sat fat.
While some people keep fighting about saturated fat being good or bad, I suggest that you don’t. There are no winners in that argument. The argument in itself is flawed, because we’re asking the wrong question.
We cannot say that saturated fat is unhealthy for most people. Or that saturated fat is healthy for most people.
Each of us is intrinsically different, metabolise nutrients differently, and respond differently to identical protocols and conditions.
In times of conflicting dietary advice, sharpening your “junk science radar” is critical. Use the list of questions I’ve given you above as smart filters when reading health news!
And if you’d like to polish up your research skills and get better at making sense of the science, we’re developing our Become a Research Pro course. You’re welcome to sign up to be notified when it goes live here.
Besides that, make it a habit to set aside 30 minutes for your Science Catch-ups every other Thursday, where I make sense of news stories by looking at the underlying research for you.
With these tools, you’ll be far ahead everyone else :-)
On a scale of 1 to 10, how do you rate your “junk science radar”? Is it polished, or does it need work?
What’s your take on conflicting nutritional advice? Which of the ‘filter questions’ we explored you want to get better at answering?
Tell us in the comments below! What you share can be very helpful to other readers, or even inspire them.
And if you know someone who remains confused in the sat-fat saga, send them this. It’ll do them good!