Low Carb Vs Low Fat Diets For Weight Loss

NutritionWeight Loss

Dec 16

Written By Dylan Dacosta

Forget the dogma — what does the actual evidence say?

By: Dylan Dacosta
14 min read

Key Points:

A breakdown of 32 controlled feeding studies with calorie matched/protein matched diets was meta-analyzed. All studies were broken down into “low carb” or “low fat groups”.

The pooled data showed a statistically significant but practically meaningless benefit in favour of low fat diets for weight loss.

This shows that as long as calories and protein are equated for, however you break up your fat/carb intake probably won’t have a meaningful impact on weight loss.

Regardless of what the diet tribes say, bodyweight is still governed by energy balance (energy in vs. energy out).

The most important macronutrient for weight management is protein due to its benefits in maintaining/building lean body mass and it’s higher thermic effect (requires more energy to breakdown/utilize).

The low carb and low fat zealots may want to pucker up and get ready to kiss their sisters. As this debate, for all intents and purposes, seems to have headed toward a tie.

Oh the age old debate between high carb low fat versus low carb high fat.

I’ve been a coach for 9 years and this topic of conversation is one that seemingly never goes away.

Diet and nutrition is really not so separate from seemingly every other aspect of human existence.

Being that “sides” get formed and partisanship seems to be their lifeblood. This is true in politics, sports, religion and yes, even nutrition.

I say this as someone who as participated in this behaviour in various ways and on various topics throughout my life. So I really do not say this to judge. I bring genuine empathy to this conversation.

I also do bring my own biases. As to act like we have no biases is to not operate within a practical framework.

But, the one thing that has effectively challenged my beliefs and ultimately changed my own mind, is real evidence.

Not what your favourite guru says. I’m talking about what research actually shows.

Which does mean that the only thing that matters is numbers and data. What also does, is our ability to interpret said data, catch our own biases in action, try to correct for them (not always easy) and to actually acknowledge two things:

1. The limitations that even the highest quality evidence has

2. The reality that we don’t know as much as we’d like to lead on. So ALL of these findings can and perhaps will change over time. Science is meant to be an ever evolving and self correcting thing.

So, with all of that out of the way, I would like to dive deeper into the some high quality evidence as to what the research actually says in regards to low carb vs low fat diets within the context of body composition.

Disclaimer: I tend to have a higher carb bias because I have worked with so many folks who are afraid of carbs as a result of all the bullshit spouted online. So with that out of the way, I am aiming to be as fair as possible in this article.

This leads me to wanting to cover an important research paper from Kevin Hall & Juen Guo from 2017.

Study Reviewed: Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition

This was a meta-analysis (which means a study of relevant studies, essentially) on controlled feeding studies that matched calories and protein, but compared different carb/fat intakes and their effects on fat loss and energy expenditure.

The reason why these factors are so crucial is because this would really be the only way to pin-point whether any macronutrient independently impacts body weight/body fat.

We know that protein does. Higher protein diets tend increase lean body mass and reduce body fat mass when compared to lower protein diets. Especially within the context of weight loss. Which is why these researchers made sure all studies involved matched protein intakes between groups.

With that being said, we often hear similar claims being made from different tribes within the fitness/diet industry.

Low carbers will tell you that carbs makes you fat, while low fat dieters will tell you that fat makes you fat.

So this study was really compiling the evidence to assess if either side was right.

Methods

This paper included 32 controlled feeding studies where subjects were provided with all their food to ensure more compliance with whatever diet they were doing.

There was 563 subjects involved, spanning plenty of diversity between BMI, sex and age.

All studies were either cross over or parallel design (Cross over means subjects would do both low carb and low fat diets with a washout period and parallel is more of a randomized control trial). This is illustrated below for a visual image.

This is important to highlight, as this would be a part of that high quality evidence I was talking about.

The fact they were controlled feeding studies that matched for calories and protein, provided and monitored all subjects with their food/eating and even housed most subjects during the trial, makes this the most compelling evidence we can get.

Because these types of trials are very expensive and hard to do, the sample sizes tend to be quite small. This makes the need to meta-analyze all of these papers even more crucial.

As we should not make large conclusions from studies with a sample size of 8 people (as some of these papers had).

But compiling all of these papers did give us a pretty solid sample size (563 people) who were all involved in tightly controlled trials.

What we will often see is some people making inferences from observational data. You could point to a population with great health outcomes and then say their diet is the cause for it.

In reality, you can’t honestly do that with great confidence. This what we would call confusing correlation with causation. As who’s to say their health outcomes aren’t just an amalgamation of countless other variables.

Human health is not solely dependent on nutrition. While, nutrition is damn important, it’s not the ONLY factor. Which is why you shouldn’t make casual inferences from observational data.

With that out of the way, let’s get back to the paper.

Dietary carb intake ranged from 1% — 83% of calories across these studies and dietary fat ranged from 4%-84% of calories across these studies. So there was some more moderate studies and some more extreme ones.

The results for energy expenditure were taken from room calorimetry (a fancy room you would stay in to measure the difference in gas exchanges to calculate energy expenditure) and doubly labelled water (that fancy water I mentioned in the metabolism study that can accurately estimate energy expenditure from urine samples).

While the results for body weight and body fat were from several different methods including DEXA scans and skin fold measurements from calipers (the things that pinch your body fat).

Results

As you’ll see below, not much of anything stood out.

When it came to energy expenditure, the low fat diets actually showed a statistically significant but practically meaningless benefit when compared to the pooled averages of lower carb diets.

*The yellow squares represent the average outcomes for each individual study. While the lines represent the confidence interval ranges. Smaller samples and higher individual variability within a study tend to yield the longer lines.*

carbs vs fats for weight loss — For example: Hall et al. 2016 had pretty similar findings between subjects in favouring lower carb. While Astrup et al. 1994 also had similar findings between subjects favouring low fat. This is why meta-analysis are crucial. Single studies can’t tell as as much as we’d like to think. If you can pool findings from similar trials, you can gather much more data from larger sample sizes in order to come to a potentially more accurate conclusion.

What this means is that although this data does support the idea that low fat diets tend to have higher rates of energy expenditure in controlled settings, the difference is essentially meaningless.

As the advantage was an average of 26 more calories burned per day from the low fat groups when all data was combined.

You will also see that some studies actually showed energy expenditure advantages to low carb diets, but on average, you can see there was a very slight edge (and practically meaningless one, in all honesty) for low fat diets here.

Next, when it came to weight loss, similar results were found.

When all the data was pooled, low fat diets averaged 16 grams more of fat loss per day. Which again, is nothing outlandish. These results were, once again, statistically significant (just meaning it’s unlikely the results were just from random chance), but the effect sizes/ results weren’t very impactful.

As you’ll see based off the plot above, some studies did show an advantage for lower carb diets. This is because some individuals responded better to energy matched, lower carb diets. There is a component of individual response here.

This just shows that the pooled averages of all studies did, once again, give a slight nudge the lower fat diets. I highlight this to remind you why no single study can really be the final word.

This is what we could call a “body of literature”.

Fitness/nutrition quacks LOVE to base their entire marketing strategy off of cherry picked science.

Even if it is not inline with the actual body of literature.

If I was a low carb die hard, I could cherry pick that Golay et al. study from 1996 and tell you that low carb diets yielded a 34 grams of fat loss per day advantage when compared to calorie matched low fat diets.

I could also do the same for the opposite side and cherry pick the Sheppard paper from 2001 and say low fat diets cause an extra 49 grams of fat loss per day advantage when compared to calorie matched low carb diets.

While both of these statements would be contextually true, extrapolating these findings out to say this makes one diet superior, would not be entirely accurate.

So this is why it’s key to watch out for any marketing that goes HARD on any single research finding and pay attention to the fine print.

With this is mind, I actually wanted to highlight findings from some of these individual papers to provide you with more context.

Individual Papers

To be fair, I want to give brief breakdowns into four of the studies above.

Two that favoured low fat diets and two that favoured low carb.

Because even with a meta-analysis of high quality studies, it’s still important to not only take the findings at face value (or just from the abstract on pubmed). There is always some additional context and nuance to understand within an individual paper.

Low Fat Advantage Papers

1. Hall et all. 2016.

This paper compared ketogenic vs moderate carb diets between 17 men who were overweight or obese (25–35 BMI).
This was a metabolic ward study (meaning all subjects lived on site during the trial) everything was controlled and monitored during entire study.
They matched protein at 15% of calorie matched diets.
Control diet was 50% carbs, and 35% fat
Keto diet was 80% fat and 5% carbs
Energy expenditure showed slight advantages for the keto diets but interestingly enough, body fat loss was basically pretty equal (actually favoured low fat slightly more in the meta)
High carb diet lost 0.5kg of fat over last 15 days of period while keto group lost 0.5kg of fat over 28 days.
Keto lost more bodyweight but that was most likely due to water weight and glycogen changes from very low carb diets (which is to be expected).
Fasting glucose was similar, fasting insulin and tryglycerides were lower in keto group but once again, that did not result in more fat loss.
All in all, no clear superior method here for fat loss but keto had a slight advantage for energy expenditure.
The raw data was not reported in journal paper, but I believe this paper showed a benefit for higher carb due to the fact the high carb intervention lost the same amount of fat in 15 days that the keto group lost in 28 days.

2. Hall et al. 2015

19 obese individuals (men & women) were in a metabolic ward for 11 days each.
5 base line days at maintenance followed by 6 days of either low fat or low carb days. All subjects did both interventions.
Protein was 20–21% for both.
Low carb/high fat was 29% carbs to 50 % fat in the diet.
Low fat/high carb was 71 % carbs to only 7.7% fat in the diet (which I will say, is a very low fat diet what I would not generally recommend).
Low carb/high fat oxidized significantly more fat during the trial but low fat/high carb actually lost an insignificant higher amount fat mass measured through the DEXA scan.
0.53 kg of fat lost in low carb compared to 0.59 kg of fat lost in low fat.
This was a short term highly controlled study that used it’s results to make mathematical models that would predict longer term weight loss.
High carb/low fat did have the advantage in the paper for body fat changes and the models did too. But, we can’t guarantee they would pan out that way long term.

Low Carb Advantage Papers

1. Kahlhofer et al. 2014

Sample of 32 young men (average age of 26) with a “normal” BMI.
This compared a moderate carb diet with low glycemic index carbs to high carb with high glycemic index carbs (50% vs 65% carbs).
Protein was clamped at 15% of diet in both groups.
They would all be overfed by 50% of maintenance for 1 week, followed by 3 weeks of dieting at half of their maintenance (50% calorie restriction) and then followed by 2 weeks of being overfed at 50% above maintenance, once again.
High carb gained 0.8 KG of fat mass during over feeding
Moderate carb gained 0.7 KG of fat mass during over feeding.
High carb lost 2.6kg of fat mass after caloric restriction.
Moderate carb lost 2.6kg of fat mass as well. All measured through QMR which is similar to an MRI.
The group that gained the most fat mass after the refeeding was 1.7kg for the high glycemic index, high carb group compared to 1.0–1.1kg for all other groups.
This showed a slight disadvantage to overfeeding at 50% above maintenance after weight loss with a high carb diet comprised of foods with a high glycemic index.

2. Bogadrus et al. 1981

This paper looked at 8 untrained, obese women (greater than 30% BF) between the ages of 25–33.
All subjects went on a very low cal diet of 840 kcal per day.
Carb containing group was 35% protein, 29% fat, 36% carb.
Carb restricted group was 35% protein, 65% fat and 1% carb (making this the most carb restricted diet we saw).
The point was to test endurance during exercise at 75% of VO2 max in both groups and changes in body composition over 6 weeks.
Carb containing group had 30.18 KG of fat on average before the trial. They lost an average of 4.8kg of fat mass during the trial which was 15.9% of starting fat mass.
Carb restricted had 32.52 KG of fat on average before the trial. They lost 5.7 kg over trial which was 17.5% of starting fat mass.
This was statistically insignificant, but did trend toward an advantage for the very low carb diet in relative fat loss.
With that being said, endurance also plummeted by 50% in the low carb group and held steady with the high carb group which was said to be due to muscle glycogen being depleted in the low carb group.

Takeaways

I’m actually going to go against my bias here. As I mentioned in the beginning of this article, I tend to have a bias toward higher/moderate carb diets. With that being said, I don’t think we should overreact to this and say high carb, low fat diets are inherently better.

Sure, the pooled averages of all these papers did give evidence for lower fat diets having a slight edge, but it’s a reach to say this proves they’re more effective.

Especially when looking at the individual variation of the results.

Sure, averages had minor advantages for lower fat, but the individual response was diverse. As mentioned above, the confidence level intervals demonstrated this.

Take the Rumpler et al. 1991 paper. The average was slightly in favour for lower fat diets in regards to fat loss, but that confidence level range was huge.

Spanning from a 106 g per day average for low fat to a 91 g per day average for low carb. Which is essentially a polar opposite difference.

This was most likely due to very small sample size (8 men). The Bogadrus paper above on 8 women, also had large confidence intervals.

So even though the averages may have given a slight nod to lower fat diets, what’s best for you, your goals and your adherence, could be a lower carb diet.

Not that I am an advocate for low carb diets (I’m surely not), I just think we can’t undervalue the role individuality here.

If you engage in a lot of high intensity exercise, then I would say a higher carb diet is probably better for performance sake.

But for weight loss/weight management, this shows that what matters most is managing your calories first and protein second.

After that, what you do with your carb and fat intake is up to you and whatever suits your goals and lifestyle best.

I’ll importantly note that this does show you do NOT need to fear or avoid carbs. That’s some utter bullshit. As evident above.

If you thrive on a higher fat diet, then low carb — high fat is probably great. With considerations to monitor your saturated fat intake and an emphasis on mono/polyunsaturated fats (especially omega 3s).

If you thrive on higher carb diet, then a low fat — high carb diet is probably great too. With considerations to monitor your refined/processed carbs and an emphasis on minimally processed and fibrous carb sources.

I think one of the biggest takeaways is that no one macronutrient is to blame for weight gain/weight loss.

As I’ve said countless times, changes in body mass will be beholden to energy balance.

I also don’t think those claims about carbs/fats will go away. Which is why I like to do these reviews. To help inform you with some evidence to make better decisions with your training/diet.

The key is to find dietary strategies that help you as an individual. If you find higher carb diets to be more satisfying and easier to manage your energy intakes, then I’d lean toward a higher carb diet for you.

But I know plenty of people who find the opposite to be true.

Averages from research will never tell us what everyone should do.

Rather, they are simply good frameworks to work off.

If you know that energy balance matters most and that protein is the most impactful macronutrient (for body composition), then this gives you a lot more freedom to explore with what works best for you.

But if you believe that you can’t eat carbs or fats and subscribe to a short list of “healthy foods”, this can really be damaging to your relationship with food and also very challenging to adhere to in the real world.

To know the former, allows you to focus on finding foods and dietary strategies that help you stay satisfied and nourished without having to completely avoid living.

And it just so happens that this usually involves basing your diet around minimally processed, more nutrient dense foods while still making room for your favourite foods.

This just goes to show that whether that basis is higher carb or higher fat, it doesn’t really matter as long as energy balanced is accounted for and especially if protein is too.

Additional Resources:

Article: How to Make Your Own Meal Plan

Check out this article for one of our most in depth resources that will help you figure out roughly what your energy intake and macronutrient splits should be based on your goals.

Also, it has plenty of practical tips that can help you devise your own meal plan for lasting success.

Podcast: The Carbs Vs. Fats Debate

Check out this episode of the podcast that Coach Sam & I did on this exact topic.

We dive deeper into our own experiences with falling into dogmatic nutrition camps.

Spotify Link
Apple Link

Cheers,
Coach Dylan 🍻

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Also, if you are looking to work with Coach Sam or I, we are accepting online coaching clients.

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References:

Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5568065/
The role of protein in weight loss and maintenance
https://academic.oup.com/ajcn/article/101/6/1320S/4564492
Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men
https://academic.oup.com/ajcn/article/104/2/324/4564649

4. Calorie for Calorie, Dietary Fat Restriction Results in More Body Fat Loss than Carbohydrate Restriction in People with Obesity
https://www.sciencedirect.com/science/article/pii/S1550413115003502

5. Carbohydrate intake and glycemic index affect substrate oxidation during a controlled weight cycle in healthy men
https://www.nature.com/articles/ejcn2014132

6. Comparison of carbohydrate-containing and carbohydrate-restricted hypocaloric diets in the treatment of obesity. Endurance and metabolic fuel homeostasis during strenuous exercise.
https://www.jci.org/articles/view/110268

7. Energy-intake restriction and diet-composition effects on energy expenditure in men
https://academic.oup.com/ajcn/article-abstract/53/2/430/4694241?redirectedFrom=fulltext

Dylan Dacosta