Low Fat Vs. Low Carb, Which is Better for Fat Loss?: Research Review

Which diet works best for fat loss? Low Fat or Low Carb? It’s an argument that’s been going on longer than “Which sandwich cut tastes better: Diagonal or Straight?” (as every sane person knows, the answer is diagonal. Duh!).

For quite a while (from around the 1960’s to 1990’s) low fat was touted as the way to go because excess saturated fat in the diet was "believed" to cause heart disease. After all, it makes perfect sense that eating fat, makes you fat, right?

That theory was followed by a stream of low fat diets and subsequently, low fat foods and diet products. So much so that fat was demonized. People love to label things as either “Good” or “Bad” (with no grey areas in between) so the demonization of fat was the natural step for people to take when they heard that “excess” saturated fat was a problem. Anyway, if those low fat diets were followed consistently, they worked. People were able to lose weight and improve their health. Yay!

Then, around the 1990s, low carbohydrate diets started to become popular based around the theory that insulin, which is released by our bodies when we eat carbs (and protein for that matter), was the real culprit behind weight gain and heart disease (which often went hand in hand with obesity). Simply reduce your insulin by reducing carbs and say goodbye to your love-handles (as you can see, people really love simple,” one or the other” solutions).

You know what happened then? Yup, carbs became demonized to the extent that fat had been (at least in some nutritional circles) and low-carb and carb-free food options grew in popularity. Lettuce wraps? Burrito Bowl? Anyone? And you know what? Those low-carb diets worked too! Yay again?

With the way people like to “take sides” on the Fat/Carb debate it’s no wonder that many people are still very confused about the best way to diet. Luckily we have science on our side to help us better answer the question.

The research paper I’m going to review, by Veum et al. is titled “Visceral adiposity and metabolic syndrome after very high–fat and low-fat isocaloric diets: a randomized controlled trial” (2017) {1}.

If you don't have a lot of time you can just skip past all the sciency stuff here to the “What does this all mean” section at the end. Go ahead, I’ll just hang my head in disappointment as you scroll past all the juicy science!

As for those of you who are still with me, let’s take a closer look at the study:

• There were 38 volunteers for the experiment. All were men between 30 and 50 years old with abdominal obesity (basically, a spare tyre) and without diabetes.
• They were divided, randomly into 2 groups: 18 were in a Low Fat High Carbohydrate diet group (LFHC) and 20 were in a Very High Fat Low Carbohydrate diet group (VHFLC).
• The diets were planned to be isocaloric (having the same amount of calories) with only a small drop in calories and to have the same content of protein and polyunsaturated fatty acids (PUFAs) (we’ll talk about these later). The planned perentage of energy for the two diet groups was as follows:

• The diets were designed to be based around the same, low-glycemic foods just with different quantities for the different diets.
• The men were instructed to follow other healthy eating practices such as:
• • Eating  more than 500g of vegetables and fruit per day
  • Avoiding highly processed foods, hydrogenated oils, added sugar and plant oils high in Omega-6 fats
  • Taking a broad-spectrum multi-vitamin & mineral supplement (provided by the researchers)
• The men were taught how to accurately measure and track their food intake using an online application that also offered interactive help on line to help avoid any discrepancies
• The men were also given detailed recipe books with meals designed for their specific nutrient content
• The diets lasted 12 weeks with the men recording their food intake for 5 consecutive days on three occasions during the experiment (once each month) and once before the experiment (for a baseline reference).
• The men were also instructed to NOT change their exercise habits during the course of the experiment.
• On top of this, the men received some food products to use during the diets, in order to make the diets more similar in food content (if not in macronutrient content).
• Before, during and after the diet, the following health parameters were measured:
• • Body weight
  • Body fat (by impedence)
  • Visceral fat and Subcutaneous fat volume (by CT scan)
  • Blood markers of metabolic health (glucose, triglycerides, cholesterol etc.)

The men did a really great job of following their diets (mostly down to all the work the team of investigators put in at the beginning, teaching the subjects what they should eat and how they should record it).

Before we talk about the results we should take a closer look at what the two groups ate and what was similar and what was different about the two diets. The average macronutrient consumption for the two groups during the experiment was as follows:

Ok, so the first thing to note from the chart above is that the diets had virtually the same amount of calories (isocaloric). This is incredibly important when comparing two diets because if the calories are different then any differences seen in the results could (potentially) be explained by that and not simply due to other differing factors in the diet.

On top of that the protein and poyunsaturated fatty acid (PUFA) content of the diets were virtually identical. This was done, once again, to ensure that the differences in the results of the two groups were caused by what the experiment was investigating i.e. the differing carb and fat contents of the diet. Both protein and PUFAs can have different metabolic effects if their relative consumption differed between groups so it’s important that they were standardized in this experiment.

Now that we’ve seen what the diets had in common. Let’s take a look at the differences because they’ll be responsible for the different results we get.

Firstly and most importantly we can see the significant difference in the carb and fat contents of the diet.

• The LFHC group ate on average 72g of fat and 281g of carbs whereas...
• The VHFLC group ate a hefty 167g of fat and only 56g of carbs per day.

From the chart, you’ll also see that the VHFLC group ate significantly more saturated fat and cholesterol than the LFHC group.

Now, let’s see how these dietary differences affected the end results.

So, you’re all dying to know which diet was best for fat loss, right? Well the answer is... drum roll please:...NEITHER!    

Yup, you read right. And just in case you don’t believe me, take a look at this summary of the results below:

There was no statistically significant difference between groups in ANY of the anthropometric (physical) measurements.

Both the Low-Fat diet group and the Low-Carb diet group:

• Reduced total body fat by 26-30%
• Reduced visceral fat by 21-27% (visceral fat is the fat stored in our abdomen around our internal organs and is associated with a lot of health problems such as metabolic syndrome)
• Lost an average of only 1kg of muscle mass (which is very impressive without exercise)
• Showed highly significant drops in blood pressure 

So that’s it? End of story? There were no differences between the two groups? Well, let’s talk about the biochemical tests.

The majority of the blood markers tested (such as insulin, glycated hemoglobin, glucagon, triglycerides etc.) all dropped significantly from baseline with no difference between the two diets. However the following chart shows the biochemical markers that did show a difference.

As you can see, there were differences in the changes in Total Cholesterol, LDL-Cholesterol and HDL-Cholesterol. Total cholesterol dropped in the Low-Fat group as did LDL (commonly known as “bad” cholesterol) as well as HDL (known as “good” cholesterol).

However, in the High-Fat group, total, LDL and HDL cholesterol all increased. While this might sound alarming at first, an increase in HDL is consiered to be beneficial and the overall ratio of LDL:HDL is considered to be more important as a marker of health. As the LDL:HDL ratio didn’t significantly change in either diet, the results are all considered to be in a healthy range.

Also, the fasting glucose only decreased “significantly” in the Low-Fat group although it did decrease somewhat in the High-Fat group, too. As the before and after values were considered to be within the healthy range, the difference in absolute terms isn’t significant.

On a final note, there was one interesting difference between the LFHC & VHFLC groups; many of the biochemical markers changed at different stages of the two diets, some earlier and some later. I won’t get into it here, but it's just an interesting observation.

This really was a well designed study for a few reasons.

1. It was designed to be isocaloric which is damn important but what’s even better is that it also had equal amounts of protein and PUFAs so they can’t be used as possible “confounders”.
2. It wasn’t designed to have a severe calorie deficit (~2200 Kcal/day) so it better imitates a more long term, sustainable diet.
3. The researchers put in a lot of work to accurately monitor the volunteers food intake (online interactive food tracking app, training for the volunteers, specifically designed recipes, healthy eating advice etc.).
4. Both groups got the majority of their energy-rich foods from the same foods, just varying in proportion, which helps to eliminate individual foods as confounders of the results.
5. The study lasted 3 months and longer term studies give much more accurate results than studies only a few days or weeks.

What all this means is that any differences between the two groups would be most likely due to the difference in fat and carb contents of the diets, which is exactly what we want to know.

No experiment is perfect so I have to mention a couple of peeves (all of which were pointed out by the researchers themselves):

1. The number of volunteers could have been higher (the more the merrier for science).
2. There was no control group for comparison to a “normal” diet.
3. All the volunteers were middle-aged men so the results may not be the same for women or different age groups.
4. With any feeding experiment that isn’t performed completely in a lab, you can never be 100% sure that the volunteers are recording their diet 100% accurately (or honestly).

Basically, this experiment showed that when eating a calorie reduced diet based around wholefoods, the proportion of fat or carbohydrates doesn’t matter. When calories are reduced, both low-fat and high-fat diets result in the same decrease in body fat (particularly the nasty visceral fat) and the same improvement in physical and biochemical health markers.

It’s also a confirmation of something that many scientists have known for years but the media won’t let die: saturated fat in a calorie controlled diet does not cause health problems. The VHFLC group ate a huge amount of saturated fat and had similar results to the Low Fat group. Many of the health benefits seen in this study came from the simple act of losing excess body-fat, which was brought about by simply reducing calories.

Well, I didn’t say that. Here’s where the interpretation of experimental results is really important. If you’re in a calorie deficit AND you’re eating a “healthy” diet AND you’re getting sufficient protein (notice all the qualifiers here?) then it’s not that important if you get the rest of your energy from fat or carbs. In fact, this means you can better customize your diet to suit your food tastes and preferences.

You can’t eliminate fat from a diet entirely because you would soon become deficient in essential fatty acids (EFAs) and start to suffer hormonal problems. Carbs, while not essential for health have other benefits that make them worth maintaining in your diet. Specifically, carbs allow you to exercise better and exercise should be part of any health-promoting lifestyle.

Besides that, carbs add a nice amount of bulk to a diet. In fact the LFHC group ate almost twice the weight of food as the VHFLC group (2.1kg Vs. 1.2kg, respectively). Not feeling hungry is damn important and having a little extra bulk in your diet from carb sources (like wholegrains, fruit, legumes etc) could really help to keep hunger at bay and make a diet more pleasant. Besides that, carbs are delicious!

On the other hand, if you were trying to gain weight, the carb/fat proportion might be a little bit more important, as it is if you do a calorie-cycling style of diet... but that’s a conversation for another day.

I’ve said it many times before, but the most important factor of any diet is consistency. The easier a diet is to stick to, long-term, the more successful it will be. As long as you’re in a calorie deficit you’ll lose weight so playing around with the amount of carbs and fats you eat will help make your diet more enjoyable, sustainable and successful.

Eat well, folks.

Bibliography

1. Veum VL, Laupsa-Borge J, Eng Ø, Rostrup E, Larsen TH, Nordrehaug JE, Mellgren G. Visceral adiposity and metabolic syndrome after very high–fat and low-fat isocaloric diets: a randomized controlled trial. The American Journal of Clinical Nutrition, 2017. 105(1), 85-99.

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