Why a low fat diet isn’t the best diet for you

Welcome to the next edition of my exploring popular weight loss diets series. My first post was on intermittent fasting here. I wanted to give an overview of the popular weight loss diets and discuss whether they’re really worth following.

In this post, I’ll be talking about a low fat diet. A low fat diet generally means less than 30% of your daily calories come from fat. It includes swapping products for their low fat or lite counterparts like low fat mayo or low fat cheese.

Is a low fat diet the best diet for weight loss? 

The simplified answer is no.

The more complex answer is that while a low fat diet may lead to weight loss, it’s due to the calorie deficit rather than the low fat aspect. And you can be in a calorie deficit without following a low fat diet.

There have also been large research studies that compared low fat diets to other diets, and the people following the low fat diet actually lost the least amount of weight. 

Fat is an essential nutrient: 

Firstly, I thought I’d discuss how important dietary fat is.

There are 4 fat soluble vitamins, vitamin A, D, E, and K. Fat soluble means they dissolve in fat and so will be better absorbed if eaten with a source of fat. These vitamins all play crucial roles within the body and a deficiency in any of them can lead to serious complications.

Dietary fat is also an important source of essential fatty acids, which our bodies can’t produce themselves. You may have heard of omega 3 fatty acids and omega 6 fatty acids, and these are the two types that we have to get from our diet. These fatty acids are needed for brain and heart health. And they may also have a protective role against a host of diseases like cancer and mental illnesses.

As you can see, following a low fat diet can leave you with nutrient deficiencies and that’s without even mentioning weight loss.

A low fat diet for weight loss: 

As I mentioned earlier, a lot of research has looked at different weight loss diets, and the low fat diet always seems to be the loser.

A study that compared a low fat diet, to a low carb diet and a Mediterranean diet showed that the average weight loss for people following the low fat diet was 2.9kg. The people following the Mediterranean diet lost an average of 4.4kg. The low carb diet followers lost an average of 4.7kg.

Another study comparing low carb diets to low fat diets found similar results. The people following the low fat diet lost significantly less weight than the others.

So, while the people on the low fat diet did lose weight, it was a lot less compared to other diets. As you can see, a low fat diet isn’t the best for weight loss.

Fat is calorie dense but satisfying:  

Fat is the most energy dense nutrient. 1 gram of fat has 9 calories. For reference, 1 gram of carbohydrate and 1 gram of protein have 4 calories each. By this logic, I can see why people would adopt a low fat diet. If you’re aiming for a calorie deficit, then cutting down on the most calorie dense nutrient can help lead to a calorie deficit.

But looking just at the calories doesn’t consider how satisfying each nutrient is and how full you’ll feel after eating a meal. Fat, particularly when eaten with a source of fibre or a source of protein leads to greater feelings of fullness.

So having a balanced meal with a source of fat can keep you full and satisfied, meaning you won't get hungry as quickly. Listening to your body’s fullness cues is a better way to manage your weight rather than eating low fat foods to save on calories.

Low fat products aren’t always ‘healthy’: 

Low fat or fat free products aren’t always healthier than their full fat counterparts. I wrote about this in my nutrition myths post last year. Fat is a great flavour carrier and so low fat products have to compensate for this. There is often more sugar or salt added to make up the flavour.

For example, Tesco’s 30% less fat peanut butter has 14.5g of sugar (per 100g) while Tesco’s regular smooth peanut butter has 6g of sugar (per 100g). This is more than double the amount of sugar in the low fat product.

Also, there are plenty of products that are naturally low in fat, but they might not be considered the most nutritious option. For example, a bag of Haribos, and Frosties cereal are both low in fat. This applies to the opposite too, there are foods high in fat that have lots of health benefits like fish, nuts, and seeds.

Aiming for a balanced diet can be a better alternative to a low fat diet. If you are wary of foods with fat, then reducing the portion size could be a better option than swapping to low fat products.

Benefits of a low fat diet: 

For the sake of balance, I thought I’d share a few positives of a low fat diet.

People following a low fat diet are associated with having lower LDL cholesterol levels. LDL cholesterol is often called ‘bad’ cholesterol. This is because high levels of LDL in the blood can increase your risk of heart disease and stroke. 

A low fat diet can also help reduce your blood pressure. While it’s not the best eating pattern to reduce your blood pressure, it does have an effect on it. If your blood pressure is too high for too long it can damage the blood vessels, leading to heart disease and kidney disease.

But again, you can lower your cholesterol and your blood pressure without being on a low fat diet. 

In my next blog post I’ll be writing more about why fat is an essential nutrient, and what happens if we don’t get enough.

Key points: 

• A low fat diet means less than 30% of your daily calories come from fat.
• Studies comparing low fat diets to other diets have shown the people lose the least amount of weight on a low fat diet.
• Dietary fat is needed for vitamin absorption and as a source of essential fatty acids.
• Fat is the most calorie dense nutrient at 9 calories per gram of fat.
• Low fat products often have more added sugar and salt to make up for the loss of flavour by removing fat.
• Low fat doesn't automatically make a food healthier, just like how something high in fat isn't always unhealthy. Like nuts and oily fish for example.
• A low fat diet is associated with lower ‘bad’ cholesterol and lower blood pressure.

 

I hope this blog post has given you the facts to make an informed choice about your food. Let me know if there's any popular diets you want me to write about next!

 

Bye for now! 👋

References:

Fat soluble vitamins: https://www.ncbi.nlm.nih.gov/books/NBK218749/

Essential fatty acids: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4190204/ and https://pubmed.ncbi.nlm.nih.gov/22435414/

Hunger and fullness cues rather than calorie counting: https://pubmed.ncbi.nlm.nih.gov/23962472/

Weight loss studies: https://www.cambridge.org/core/journals/british-journal-of-nutrition/article/verylowcarbohydrate-ketogenic-diet-v-lowfat-diet-for-longterm-weight-loss-a-metaanalysis-of-randomised-controlled-trials/6FD9F975BAFF1D46F84C8BA9CE860783 and https://www.nejm.org/doi/10.1056/NEJMoa0708681?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub++0www.ncbi.nlm.nih.gov and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7190064/