Apr 30, 2022 / by Jon Bellis / No Comments

Does fat make you fat? This was certainly the received wisdom for decades. We were told that a low-fat diet was the way to avoid weight gain. Yet, in the years that followed that guidance, obesity levels have continued to rise. The low-fat approach has been seen as a failure.

Instead, carbohydrates are often demonised, and low-carb diets are all the rage. Of course, low carb diets tend to be high in fat so are, in effect, high-fat diets.

You’ll find advocates of both high-fat and low-fat diets all over the internet. You’ll also find the advocates citing scientific research proving that their approach is best for weight loss or health. And on top of that, there are countless dietary patterns with different amounts of fat or carbs, some restricting certain foods or espousing an emphasis on others. No wonder there is confusion about healthy eating and weight loss.

So, what’s the truth? Does fat make you fat? Is there even a truth, or is the jury still out? In this post, we look at dietary fat, present some facts and give you our view.


Current guidance


UK Government

When a country’s government makes nutritional recommendations, you can be sure that they are well researched and agreed upon by a panel of industry experts. And so it is with the UK government.

Here are the current recommendations

  • Fat: less than 35% of calories
  • Carbs: at least 53% of calories
  • Protein: 9% of calories
  • Fibre: 30g a day

First of all, you’ll see that carbs are relatively high, at 53%. That corresponds to 333g of carbs per day for a typical male. That’s not a low carb diet. A low-carb keto diet, for example, will often advocate carbs as low as 50g per day.

Second, notice the wording. For carbs, 53% is your minimum, and the choice of words encourages you to have more than this. And for fat, 35% is your maximum, but this time the words are encouraging you to keep it below this upper limit.


US Government

That’s the UK government. What about the US? Their excellent publication ‘Dietary Guidelines for Americans’ looks pretty similar for adults aged 18-51

  • Fat: 20-35%
  • Carbs: 45-65%
  • Protein: 10-35%
  • Fibre: 25-28g

The upper limit for fat is still 35%, but it goes as low as 20%. That means an intake as low as 20% is still deemed safe and healthy. Notice also that the lower limit for carbs is 45%, which is by no means a low-carb approach, especially by keto standards.


World Health Organisation

The World Health Organisation (WHO) also has dietary recommendations. The advice is to limit fat to 30% of calories to ‘avoid unhealthy weight gain’.



And finally, another well regarded and well-researched diet is the DASH diet, designed to reduce blood pressure. It has the following macronutrient aims

  • Fat: 27%
  • Carbs: 55%
  • Protein: 18%
  • Fibre: 30g

It looks familiar, doesn’t it?


Food groups

These diets all have something else in common: advice on food groups. In fact, the US guidelines now emphasise food groups rather than macronutrient quantities. These guidelines can be summarised as follows:

  • Lots of vegetables
  • Lots of fruit
  • Plenty of whole grains
  • Good amounts of legumes
  • Moderate intake of lean protein
  • Moderate intake of low fat or zero fat dairy
  • Some nuts and seeds
  • Fats derived from healthy sources
  • Limited saturated fat intake
  • Controlled salt intake
  • Limited refined grains and sugary foods

A colourful variety of fruit and veg. These foods are vital for optimal health

Getting plenty of variety is also a vital component of these diets for optimal health.

So, in summary, here are four well-researched dietary recommendations. They all recommend fat intake below 35% of calories and carb intake averaging 55%. You might think that these diets’ key concern is health, and they are not designed for weight loss. But if you read the recommendations, you’ll see that preventing obesity is a primary health concern and that these diets do indeed promote the attainment of a healthy weight.


Why do we even need fat in our diet?

The four diets listed above have minimum fat intake levels — the WHO goes as low as 15%. But the minimum is not zero. That suggests dietary fat intake is needed for health. But why? Here are the three main reasons. To:

  • Help with the absorption of fat-soluble vitamins A, D, E and K.
  • Help maintain healthy cholesterol levels.
  • Provide essential fats such as omega 3 and 6, which cannot be made in the body.

That’s it. Notice that ‘fuel source’ is not listed. You don’t need to consume fat to give you energy, you can make the stuff, and you’re very good at it.

You may also have spotted that the fats you do need for health are the unsaturated ones. It’s controversial whether there is a dietary requirement for saturated fat. It’s been shown in some studies to enhance testosterone production, for example. And there are different types of saturated fat, some of which may be healthy and others which a definitely not. But far more often, it’s been associated more generally with various health conditions such as heart disease and Alzheimer’s. That’s why all these diets recommend limiting saturated fat intake to 10% or below.


High-fat diets and health

Before we look at high-fat diets and body weight changes, let’s examine them from a health perspective.


Saturated fat

First of all, if you consume a high-fat diet, you will have trouble keeping your saturated fat intake below the recommended 10% of calories. Even the healthiest fat sources contain saturated fat, such as olive oil, nuts, and avocado. The higher your fat intake, the more likely you will exceed the maximum saturated fat guidelines, especially if you’re taking in less healthy fat sources.


Lowered nutrient intake

Next, if your fat intake is high, you have less room within your calorie allowance for all the foods advocated in the four healthy diets. That means fewer health-giving vegetables, whole grains, legumes and fruits. It’s those foods that are the most beneficial in all those diets.



Third, if you’re worried about saturated fat intake, you may want to load up on healthier fats. But be aware that high intakes of polyunsaturated fat are associated with reduced testosterone. You can’t win: however you mix it up on a high-fat diet, there are health implications.


Other health implications

Fourth, high-fat diets induce chronic low-level inflammation and are associated with several other health conditions. In particular, they are associated with liver insulin resistance.


High-fat diets and weight change

Let’s look at some features of dietary fat that are relevant to weight change


It’s easy to underestimate and overconsume

Fat is very calorie-dense. That means it packs a lot of calories without taking up much volume. For this reason, it’s a lot easier to overconsume fat calories. Either you overeat in an attempt to fill your stomach and feel satiated, or you misjudge the calorie content of your food because it doesn’t look like much.

Unless you weigh and log your food, you’re more likely to overconsume fatty foods. For example, we’ve had a recent discussion with someone who was putting coconut oil into her morning smoothie. Although she was using a teaspoon, she was scooping up a big blob of coconut oil, probably 3 or 4 teaspoons worth. That’s the difference between 45 calories and 180 calories. Even the blob doesn’t look like much, but it certainly packs a lot more calories than a standard teaspoon.

As another example, consider a portion of fish. A portion of white fish like cod will come in below 100 calories. On the other hand, salmon will come in at over 200 calories. In terms of portion size, they look the same, and it might be typical to swap them in and out as if they have the same number of calories. But rest assured, if oily fish is your go-to protein source, you’re much more likely to gain weight.

A tin of sardines on wooden backdrop. Too much oily fish can make you gain weight.


It’s not very satisfying

Foods that fill you up tend to have

  • Protein
  • Fibre
  • Liquid

These properties were captured in a measure called the fullness factor. You’ll see that dietary fat does not feature. So, if your diet is high in fat, it’s more likely to be low in fibre, and it may also be low in protein. You’re going to feel less satisfied because you’re missing the fibre. And because high-fat foods do not occupy much space and swell your stomach, you’re also not going to feel as full.

So, a higher fat diet will leave you unsatisfied, hungry more often and more likely to overeat.

If you’re a keto advocate, you’ll be shouting at your screen when reading that last paragraph. Because keto reduces your insulin output, it’s good for keeping feelings of hunger at bay. Or it is in theory. I spent a year on keto, and I was hungry all the time. I was unsatisfied with my meals and found it difficult to estimate and keep in check my calorie intake.

It’s no coincidence that the filling foods – whole grains, vegetables, fruits and legumes – are all featured heavily in the four healthy diets described earlier. These are all fibre rich foods and packed with nutrients. Reduce them in favour of fattier foods, and you decrease the filling fibre and the health-giving nutrients.


Fat has a lower thermic effect

The processing of your food requires energy and releases heat. When you eat, you tend to heat up. This is known as the thermic effect of food (TEF). TEF depends on the macronutrient.

  • Protein has a TEF of 20-30%
  • Carbohydrate has a TEF of 5-15%
  • Fat has a TEF of 0-5%

So, not only does fat have over twice the calories of protein and fat per gramme, but it also has virtually no thermic effect, so you’re not going to ‘waste’ any calories consuming it. In contrast, 20-30% of the calories you consume from protein are used in its processing. You can think of the actual number of assimilated calories for protein as being a lot less.


You may lose muscle

Fat plays much less of a role in favourable body composition change. On the other hand, protein and carbohydrate both have well documented anabolic properties. In other words, they will tend to help you gain or protect muscle. You’re better off using your calorie allowance to maximise the effects of these two macronutrients.

Yes, saturated fat has been shown to improve testosterone levels. But that doesn’t mean you need to load up on it, especially if you care about your long term health. And it’s also true that high intakes of polyunsaturated fat have been shown to reduce testosterone. But, again, you don’t need to go overboard on polyunsaturated fat just because it’s healthy.



Before we end this section, let’s mention keto. You’ll find plenty of literature espousing the benefits of a keto diet. And you’ll see explanations of how a keto diet will not reduce your performance in the gym and will preserve your muscle. While I can’t argue with the research papers, it certainly wasn’t my experience after spending a year on keto.

However, let’s assume that you can preserve your muscle on a keto diet. You still have to sustain low enough carbs to go through the horrible adaptation phase, become ketogenic and then maintain it. For most people, that’s too much discipline and sacrifice. For the majority, their higher fat diet is simply the way they eat, and they haven’t put much thought into it. In this instance, you’ll be missing out on anabolic opportunities provided by carbs and protein. That will reduce the amount of muscle you could have. And, of course, less muscle means a lower metabolism and fewer calories being burned over 24 hours. That’s not going to help in the fight against weight gain.


You may mistake healthy for low calorie

Avocado and guacamole. Does fat make you fat?

Just because some high-fat foods are healthy, it doesn’t mean you should shovel them in. More is not better in this instance. The following foods are often overconsumed because they are seen as healthy.

  • Oily fish
  • Olive oil
  • Coconut oil
  • Nuts and seeds
  • Avocado

You don’t need lashings of any of these. For example, the recommendation for oily fish is once or twice a week. You should use teaspoons or one-cal sprays for olive oil, and you should weigh or count your nuts. Definitely include them in your diet, but be very portion aware.

An assortment of nuts. Does fat make you fat? You should count your nuts


Fat is easy to store

Fat is the body’s preferred fuel store. So, it’s no surprise that the storage of dietary fat is a very efficient process, requiring little energy. In contrast, converting carbohydrate and protein into fat entails an energy-requiring process.

Excess calorie intake in the form of fat is going to get stored. In contrast, excess intake of the other macronutrients is more likely to be put to good use. Have you ever noticed how you heat up or have more energy after a good carbohydrate feed?

Now, it is true that the macronutrients tend to be used in the ratio of their dietary intake. So you will burn more fat for energy if you have a higher fat intake. And you’ll burn more carbs if you have a higher carb intake. So, you’ll burn what you take in if you’re in calorie equilibrium. But once you hit calorie surplus, if your excess is from fat, you’re far more likely to store that fat. If your surplus is from carbohydrate, you may instead heat up, feel more energetic and burn more calories being active.



Does fat make you fat?

So, does fat make you fat?

If I had to give a one-word answer, I’d say yes for the reasons outlined above.

But the longer answer is that a higher fat intake increases your risk of becoming overweight. If you are very much in control of your eating or weigh and log your food, you may maintain a healthy weight on a higher fat diet. You may even find a way to get all the healthful nutrients you need for optimal health.

But most people don’t have that level of awareness or control. It’s better to adopt the approach advocated in the four healthy diets outlined earlier. Fill your face with vegetables and fruits, get plenty of legumes and whole grains, choose lean protein sources and low-fat dairy, then throw in some nuts and seeds and healthy fat sources to finish it off.

Finally, be very fat aware. Know your fat sources, reduce your purchases and usage of high-fat foods and choose wisely from menus.

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