Fats were once demonised in the same way that carbohydrates are today.
What is considered the first real diet book by some, dates back to May 1863. William Banting wrote his recommendations for weight loss in “a letter of corpulence” from his own experience of being overweight and then losing a lot of weight. He opens with this paragraph:
“Of all the parasites that affect humanity I do not know of, nor can I imagine, any more distressing than that of Obesity, and, having just emerged from a very long probation in this affliction, I am desirous of circulating my humble knowledge and experience for the benefit of my fellow man, with an earnest hope it may lead to the same comfort and happiness I now feel under the extraordinary change,—which might almost be termed miraculous had it not been accomplished by the most simple common-sense means.”
The common sense he’s talking about is switching his diet of bread, milk and buttered toast for meat and fruit with some vegetables and dry wine. This diet provided the basis for many diets and fads to come. As dieting became more popular the low fat fad began to gain popularity, especially amongst women who weren’t even overweight in the first place. Counting calories was the way to do it and because it was known that fats contain 9 kcals per gram and protein and carbohydrate only 4, the obvious way to reduce calories appeared to be cutting out fats.
Popularity for this diet continued to grow as a result of poorly conducted research on cardiovascular health. From 1980 onwards, having been promoted by doctors, the government, the food industry and also the media, the low fat diet was the way to go if you needed to shred some pounds. A clear causal relationship between the low fat diet and heart disease or even weight loss is to date, not established. Ironically, the population of Western countries only became more overweight during these years.
More recently, the reputation of fats has improved massively. The low carb diet has overtaken the low fat diet as the latest diet trend and the market for artisan nut butters providing healthy fats has exploded.
So what is dietary fat and why do we need it?
Fats are the most efficient macronutrient our bodies can use. Dietary fat packs in 9 kcals per gram, so it’s a very energy dense nutrient. As previously explained it’s also an efficient storage nutrient. Therefore, we store excess energy, regardless of whether this comes in the form of protein, carbohydrate or fat, as fat rather than glycogen for example.
Aside from being a great energy source, fats have many important functions. They are required to absorb some micronutrients such as fat soluble vitamins A, D, E and K, and serve as building blocks for our cells and some hormones, predominantly sex hormones like testosterone and oestrogen. This is particularly important if you lift weights because both hormones are important for muscle growth. We also need fat for good brain, heart and eye functioning in particular.
Types of fat
There are 3 types of fats: saturated (SFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA). The level of saturation refers to the amount of hydrogen atoms present in each molecule. A saturated fat has all their carbon atoms covered or “saturated” with a hydrogen atom. A MUFA is short on one hydrogen atom and instead has a double bond. This double bond causes the structure of the molecule to bend. A PUFA is short on multiple hydrogen atoms and has multiple double bonds, therefore, the molecule is bent in multiple places. This bending of the molecule has consequences for the properties of the fat and how it behaves in the body. It is the reason PUFAs tend to be liquid, and SFA’s are solid at room temperature. Unsaturated fats are found mostly in plants and saturated fats mostly in animal products, but most foods will have a bit of both.
SFA rich foods: meat, eggs, full fat dairy and cheese, coconut and palm oil
PUFAs: walnuts, seeds, fatty fish, soybean oil and safflower oil
Some fats are essential. This means our bodies cannot synthesise them. Most fats can be synthesised but there are 2 types you need to eat. I’m sure you’ve all heard of the PUFAs omega 3 and 6.
Omega 6’s are linoleic acid (LA) and arachidonic acid (AA). LA is found in vegetable oils mostly, and AA in animal products like fatty meat, eggs and dairy. Our bodies can convert LA to AA.
Omega 3 fatty acids are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoicacid (DHA). ALA is found in canola oil, walnuts, soya, green leafy vegetables and flaxseeds and EPA and DHA only in fish really. Dietary ALA can be converted to DHA and EPA.
The average Western diet is high in omega 6 and low in omega 3. It turns out that it’s not so much the exact quantities but the balance between both types of fat that’s important. The ideal ratio is 1:1 respectively, but the average Western diet often has a ratio closer to 20:1. Omega 3 and 6 fatty acids have very different and opposing functions in the human body therefore if the balance is off, it can cause problems. Even though our bodies can convert ALA to EPA and DHA, the process is slow and inefficient. Because the conversion of LA to AA uses the same enzymes, if the diet is high in omega 6, this will have a negative effect on the conversion rate of DHA and EPA because both fatty acids will have to compete for the same enzymes.
DHA and EPA are very important for the healthy functioning of the brain but also for the heart and eyes. The best way to get these is through fish, which is why vegans and vegetarians need to pay extra attention to their fat intake. The recommendation for EPA and DHA for adults is to get 900 mg per week which is about the amount in 2 portions of fish of which at least one should be from a fatty fish, but the content will vary per species. Mackerel, salmon, trout and (fresh/frozen) tuna are good sources of these.
Good and bad fats
Unsaturated fats are what we’d refer to as “good” fats and saturated fats are classified as “bad”, however, this oversimplifies things. Rather than looking at the type of fat, it’s more useful to look at the source from which you’re getting the fats from. A better definition of a “good” fat would be the type of fat you get from whole, unprocessed foods and “bad” fats would be those found in processed foods.
“Bad” fats are mostly “man made”, for example trans fats, hydrogenated fats and margarines. Trans fats are often used in the food industry to preserve foods, improve mouthfeel and because they are more stable. It’s great from an economic point of view but not so great for your health. As mentioned earlier an unsaturated fatty acid is normally bent. Hardening a fat, which is what happens to create a trans fat, straightens out the molecule which changes its function it the body. On a side note, some trans fats are present naturally in foods, but these quantities are not nearly as much as the quantities found in processed foods.
Saturated fats have been demonised a lot and they can be unhealthy if consumed in excessive amounts and out of balance with unsaturated fatty acids. Research has linked them to a range of diseases like obesity and cardiovascular disease. However, these are all correlation studies. A clear cut connection between a high saturated fat intake and cardiovascular disease has not been established to date. Research into other health risks from high SFA intake is not consistent. However, the fear of saturated fats is deep rooted, and government food guidelines still recommend to limit this to no more than 30g for men and 20g for women in the UK, per day. If you eat a balanced diet based on whole foods it is difficult to obtain excessive amounts of saturated and trans fats in your diet.
Take home message
Fats are the most energy dense nutrient we can use, and some fats are important to maintain good health. However, even “good” fats contribute substantially to your energy balance, so if your goal is fat loss, you may want to take it easy with the avocado and peanut butter. Just because a food is healthy, doesn’t mean you can eat endless amounts of it. The energy balance is still the leading factor for fat loss. The opposite is also true, if you didn’t eat any fat, due to their importance in essential bodily functions, at some point you would die.
So the bottom line is, we need dietary fat, but if your goal is fat loss remember to track how much you’re consuming. If you are looking for health benefits or trying to avoid risks of excessive intake, I’d advise you to focus on the fat source rather than focussing on unsaturated and saturated fats. Eat a variety of whole foods to ensure you get different types of fat and be mindful of your portion sizes.