For fifty years, scientists told us that too much saturated fat was bad for our hearts, and advised us to switch to polyunsaturated fats instead. Oops.
It turns out that polyunsaturated fats are not all equal, and some of them actually increase the odds of cardiovascular disease and death.
In this week’s Research Review, we’ll explore why mistaken conclusions in science can sometimes become accepted wisdom – and which fats you really should eat for better health.
Ever notice how a particular food can become all the rage – only to drop out of fashion a few years later?
And how the food or nutrient that our doctors told us to get more of in 1990 can morph into the one they are warning us against in 2013?
It’s enough to harden a person’s arteries.
With so much conflicting information out there, it can be tough to figure out what to believe.
But as you’ll learn in this article, health is about balance. Too much or too little of any nutrient can lead to trouble.
Keep that in mind as we explore the complicated world of fats and their role in heart health.
What fats should I eat?
In the last half of the 20th century, doctors and nutrition professionals agreed: too much saturated fat was bad for the heart.
The recommendations were clear: If you want to avoid heart disease and keep your arteries free of build-up, you should increase polyunsaturated fats and decrease saturated fats in the diet.
That’s what they told us – and most of us listened.
But lately, there’s been a shift in scientific understanding.
- Saturated fats don’t seem to be as bad for us as doctors used to think.
- Polyunsaturated fats are not equal in their effects.
- And the type of polyunsaturated fat you eat may be just as important as how much of it you eat.
Keep fats real
Here’s one simplified way to understand the relationship between some different fat types.
Notice that generally, fat type alone doesn’t determine the healthiness — rather, healthy fats are found in whole, unprocessed foods, while unhealthy fats are found in processed foods.
For example, you’ll notice that naturally occurring saturated fats (such as coconut) are important in a healthy diet. On the other hand, artificially created saturated fats (fats that start out unsaturated and are then chemically processed — for instance, through hydrogenation — to become saturated, such as margarine) are not as healthy a choice.
Our bodies know what to do with real food. They don’t know what to do with the other stuff.
Keep fats in balance
Here at PN, Dr. John Berardi has long recommended getting:
- 1/3 of your fatty acids from saturated fats;
- 1/3 from monounsaturated fat; and
- 1/3 from polyunsaturated fat (with a good amount of omega-3 fatty acids)
Of course, these should mostly come from whole, unprocessed foods. (We’ll give you some ideas below.)
Want to know why omega-3 fatty acids are special, check the Research Review: How do omega-3 fatty acids work?
Every once and awhile a food or nutrient gets vilified. (By food I mean anything that has been around for at least 100 years. Low fat, low cal, low-sugar cookies — not food.)
But the truth is, there’s really no such thing as a “good” food or a “bad” food. And almost anything we swallow can be good or bad for us, depending on whether we have a deficiency or a massive overabundance.
Don’t believe me?
Let’s take a look at water. Pure, innocent, cornerstone-of-life water.
You’re mostly water – about 70%. You need water daily to live. So water is good, right?
But even water can kill you. If you over-hydrate yourself you can get water intoxication. Too much water causes a decrease in key electrolytes that are really important for important things like your heart pumping.
And of course, your lungs like to be moist but not full of water.
Again, it’s all about balance. The right amount in the right place at the right time.
Finding fatty acids in the grocery store
Now you know which fats you should eat in what proportions. But there’s no “fat” aisle at the grocery store, and most nutrition labels don’t classify fats beyond telling you whether they’re saturated or unsaturated.
Here’s how to recognize what kind of fats you’re buying and eating.
- Saturated fats come mostly from animal fats (e.g. butter, meat fats) and tropical oils (e.g. coconut oil). They’re usually solid at room temperature.
- Monounsaturated fats come mostly from avocados, nuts, and olive oil.
- Most other oils are polyunsaturates.
Start with whole foods
If you’re looking to add good fats to your diet, start with whole food-based fats in their natural, least-processed state. This includes things like:
- fatty fish and seafood; sea vegetables
- raw nuts and seeds
- fresh olives
- fresh coconut; raw cacao
- pastured butter and full-fat dairy
- fatty meats if pastured / grass-fed
Choose cooking oils wisely
Unless you’re grinding and pressing your own olives or seeds, remember that all oils have undergone at least some processing.
Look for “cold-pressed” or “extra-virgin” varieties of oil where possible.
The table below (source) breaks down the fatty acid composition of different types of oils that can be used for cooking – along with butter, for comparison. Highlighted oils are lower in omega-6 fatty acids.
Notice the smoke point of the various oils. That’s the temperature at which they begin to burn.
When you’re cooking, you want to prevent oil from burning because overheating causes chemical deterioration and produces toxic compounds that circulate in your body and lead to inflammation. Not good.
Cooking with oils high in omega-3 fatty acids is a bad idea because these oils are especially sensitive to heat, and break down easily into trans fats.
To recap: For many years, conventional wisdom held that polyunsaturated fats were good for the heart.
Recall, also, that omega-6 fat (linoleic acid) is a type of polyunsaturated fat.
So what happens when people with coronary heart disease increase omega-6 fatty acids (linoleic acid) in their diets? Today’s research review seeks to answer that question. And the answers may surprise you.
Ramsden CE, Zamora D, Leelarthaepin B, Majchrzak-Hong SF, Faurot KR, Suchindran CM, Ringel A, Davis JM, Hibbeln JR. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ. 2013 Feb 4; 346:e8707
First surprise: This study is more than 50 years old! True, it was published just this year, but the raw data was collected between 1966-1973.
Typically in science we tend to put the highest value on the most recent discoveries. Yet here, a collection of old data has given us new insights. And in some ways, the age of this study may even be an advantage. Hindsight allows us to put its findings in context.
That’s precisely what the researchers here attempted to do. They took raw data from the Sydney Diet Heart Study and re-evaluated it in light of recent mortality data for coronary heart disease and cardiovascular disease, hoping to learn what kind of fats are really good for the heart.
The original Sydney Diet Heart Study involved a total of 458 men between the ages of 30-59, each of whom had suffered a recent “coronary event.” Coronary events included acute myocardial infarction (86%) and acute coronary insufficiency or angina (14%).
- The average age was 49, and the average BMI was 25, which is borderline overweight.
- Their total blood cholesterol levels were high (281 mg/dL on average), but there’s no data on the subtypes of cholesterol (LDL vs. HDL).
- Their blood triglycerides were considered borderline (at 187.5 mg/dL on average).
- Blood pressure was at the high end of normal (at 136/89 on average).
- Most of the subjects smoked (about 70% admitted to this) and fewer than 7% had diabetes.
About half the men (237) were assigned to a control group. Researchers didn’t ask them to change their diets in any way, although some voluntarily stopped using butter in favor of the (supposedly) healthier margarine.
Meanwhile, the rest of the participants (221) were asked to make two changes.
- First, they ate more polyunsaturated fatty acids (PUFA), aiming to get about 15% of their daily calories from these fats.
- Meanwhile, they reduced their saturated fatty acids to less than 10% of their daily calories and tried to keep dietary cholesterol to less than 300 mg per day.
Even today, many doctors would give you similar advice.
Subjects continued with this regime for up to seven years. The median length of participation in the study was three years.
To get their PUFA intake up, researchers gave the men safflower oil and margarine (aka solid safflower oil) for their cooking needs.
Both groups got advice to stop smoking and to lose weight.
This might be the first instance of dramatic irony I’ve seen in a recent research study.
Two things we know today, that nobody knew or cared about 50 years ago:
- Margarine contains trans fats.
- Trans fats are bad for you.
It wasn’t until the 1990s that eating margarine containing trans fats was linked to heart disease (2). Whoops.
The authors of the original study (3) hypothesized that eating more polyunsaturated fat would contribute to lower levels of saturated fat in the diet. Lower levels of saturated fat would, in turn, decrease cardiovascular risk factors such as total cholesterol and total triglycerides.
Ultimately, they believed that this would reduce the incidence of cardiovascular and coronary disease and lead to lower death rates.
True to their expectations, 12 months after the study’s start, the intervention group showed more significant changes than the control group in the following dietary and blood measures:
- polyunsaturated fat intake (↑)
- saturated fat intake (↓)
- total cholesterol intake (↓)
- total blood cholesterol levels (↓)
- total blood triglycerides levels (↓)
In other words, one year into the Sydney Diet Heart Study, all findings supported the original hypothesis.
Four years later, it was a different story.
By then, it had become clear that the intervention group was experiencing higher death rates, higher rates of cardiovascular disease and higher rates of coronary disease!
In the original study – published in 1978 – researchers did report these findings. But they didn’t try to explain what had caused the increased death rates (4).
Why? We don’t know for sure. But it’s possible that these findings confused them, because they went against accepted wisdom.
How could a clear decrease in cholesterol be linked to higher rates of cardiovascular and coronary disease? It didn’t make sense, given the state of knowledge at the time.
Looking back at other studies
In the meta-analysis under review, the scientists scrutinized a number of other, similar studies to try to figure out what caused the increased death rates in this particular study.
Their review of eight different papers revealed that the type of polyunsaturated fats used in an intervention seemed to be key.
Increasing omega-6 oils exclusively in an intervention seemed to lead to a higher risk of cardiovascular disease and death. Using mixed omega3/omega-6 polyunsaturated fats actually decreased these risks.
There are two main conclusions we can draw from this study:
- Eating more polyunsaturated fats in the form of omega-6 fatty acids increases rates of death, cardiovascular disease, and coronary disease.
- Science is context-dependent.
If you follow PN, the first conclusion – that eating more omega-6 fatty acids could increase the risk of disease – won’t come as a huge surprise. You already know that some omega-6 fats have been linked to inflammation. (See All About Bad Fats.)
But for many people, this is big news. And after years of being told by doctors, nutritionists, and the media to eat vegetable oils high in polyunsaturated fats, they’re understandably confused and exasperated.
Our second conclusion, that science is context dependent, can help us make sense of this.
Most of us tend to imagine that science proceeds in a linear fashion. Start with an idea (hypothesis), gather data, interpret the data, and presto-bingo, you have the answer! Or, even more misleading, you have Truth.
But that’s not really the way that scientific knowledge advances.
In the Sydney Diet Heart Study, researchers hypothesized that more polyunsaturated fats would decrease death due to cardiovascular and coronary disease, and that cholesterol is a good measure of predicting coronary disease.
If you look at the data today, with the benefit of hindsight, it appears that hypothesis was wrong.
But back in 1970, all other available data supported a diet low in saturated fat, high in unsaturated fat, and low in cholesterol. And researchers agreed that this was the type of diet that was best for heart health.
It’s almost impossible to publish data that refutes the accepted wisdom in a given period – especially if you have no plausible explanation for your anomalous results. And the results of the original study were, quite simply, impossible to interpret, given what the scientific community knew and accepted in 1970.
Fast forward to 2013.
With the advantage of 50 years further study and experimentation, we know that not all polyunsaturated fats are equal.
Omega-6 polyunsaturated fats, in particular, can increase the risk of death from coronary disease – probably because they increase inflammation.
But in 1970, scientists didn’t distinguish between the sub-types of polyunsaturated fat, and didn’t recognize that cholesterol is not a good measure for predicting coronary disease.
That’s why, in the end, it’s important to understand that science is a process. Knowledge builds over time.
This is why we shouldn’t jump on every nutritional bandwagon; sometimes we need context to make sense of recent discoveries. Common sense and patience are key.
There are no “good foods” or “bad foods” and no good or bad nutrients, either. Eating whole foods is always the safest (and healthiest) bet.
So whenever you hear somebody speak in absolutes about a particular nutrient (e.g. “Carbs are bad for you”, or “No one should ever eat saturated fat”) it is best to take this suggestion with a (healthy) serving of salt.
The Sydney Diet Heart study revealed the uncomfortable truth that diets high in one type of fat (omega-6 fatty acids, particularly from processed sources like cooking oils) contribute to higher rates of death from heart disease.
But the solution is not to base your diet on another type of fat.
The healthiest diets include a balance of different fatty acids, ideally from a diverse diet of whole, unprocessed foods.
Keep it simple. Keep it real. Keep it in balance.
Putting it into practice
Today, look at your fat intake. What could you get more of? What could you get less of?
Make small changes to keep it simple, real, and in balance.
Choose whole foods.
Decrease your intake of processed fats.
Get more omega-3 fatty acids, ideally from fish or other marine sources.
Here’s an interview by the editors of the British Medical Journal with Christopher E. Ramsden, the senior scientist in the study under review. (The interview starts at 17:43).
He briefly discusses polyunsaturated fats, the study findings, how the researchers recovered data, and the possibility of re-examining paradoxical findings from the past in light of current knowledge.
And for more from PN, Ryan Andrews has written several All About articles on fats and oils that will add to your understanding.
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