What’s The #1 Diet For Fat Loss? Low-Fat Diets vs Low-Carb Diets

As someone who has struggled with weight myself, writing this post wasn’t necessarily fun. I remember being about 40 lbs heavier 3 years ago (at my heaviest I was 185 lbs) and people casually bringing my weight into everyday conversation like, “you’d look really good if you were athletic”, or “you should try to loose that baby fat” and so on. After a series of similar social encounters I decided that I will make drastic changes to my unhealthy diet and start exercising regularly, all of which together helped me shed that extra weight and more importantly has helped me keep it off since.

Now 4 years later, the days of my weight loss struggles behind me, I had the opportunity to attend a seminar by none other than Dr. Kevin Hall. He is currently the chief of integrative physiology section at the National institute of health (NIH, USA) and has authored over a 100 publications, mostly studying the process of weight loss and how the human brain adapts to it. His seminar was titled “The calculus of calories”, exemplifying the fact that his take on physiology/weight loss research was different, given he trained as a physicist (yea, a physicist). He started the seminar by debunking weight loss myths, which I’m gonna talk about in this blog post (with data, so you guys understand the hundreds and thousands of weight loss texts out there, without credible data are probably garbage).

The first one he talked about was the classic rule which is a central tenet of every single dietitian’s manual; that 1 pound of fat = 3500 calories and if you cut 500 calories from your diet daily then after 7 days (7×500=3500)  you will lose 1 pound of fat. This rule is so magical and so completely ludicrous that if put in action for a course of 2 years in a 100 kg man, it would make him disappear! The reason this rule is scientifically untrue is that it assumes that when you subtract 500 calories from your diet nothing else changes in the body BUT fat and you ONLY lose fat tissue. It also assumes that when you cut calories, the body doesn’t have any pullback on your weight loss and it lets you drop fat, again not true. The body resists weight (fat) loss and if you’re ever advised that cutting 500 calories daily would lead to a steady loss of 1 pound of fat/week, it’s just simply not true (Quantification of the effect of energy imbalance on body weight, Lancet, 2011)


The other myth he debunked was The low-fat versus low-carbohydrate diet divideand which one is better for fat loss (fat loss because that’s what you wanna lose, the fat and no necessarily your muscle mass). The low-fat versus low-carb battle has been thrown into sharp focus for at least a couple of decades now. On one end, there are proponents of the low-carb diet like journalist Gary Taubes and Dr. Peter Attia (who fervently supports the low-carb diet phenomenon by wearing shirts that say “Praise The Lard”). On the other end, there are supporters of the low-fat diet (not Paula Deen, she loves butter), who also like their low-carb enemies have made a fortune on selling diet manuals, recipe books and fat blocking supplements.


Low-fat diet proponents say that you if eat less fat, you accumulate less fat, there’s no science and it’s just simple logic, dummies. The low-carb diet fad however comes with its own scientific model, it’s a package deal.

The scientific model behind the low-carb diet is the carbohydrate-insulin hypothesis which has been extensively promoted. It suggests that a diet heavy in carbohydrates (especially refined grains and sugars) leads to fat gain because of a specific mechanism: Carbs drive up insulin in the body, causing the body to hold on to fat and suppress calorie burn. According to this hypothesis, to lose fat you reduce the amount of carb calories you eat and replace them with fat calories. This is supposed to drive down insulin levels, boost calorie burn, and help fat melt away…instead of just cutting calories, you’re supposed to change the carb calories to fat calories. So which one works? The low-fat diet or the low-carb diet?

To exactly figure out whether a low-fat or a low carb diet is better for fat loss, Dr. Hall’s group designed a controlled study. 17 overweight/obese men were admitted to metabolic wards (a chamber where you can monitor an individual’s macronutrient intake and other output biological parameters like body composition, energy expenditure, metabolic fluxes etc.), where they consumed a low-fat baseline diet for 4 week followed by 4 week of an isocaloric low-carb diet with the same protein content.

The findings of the study were startling. The subjects lost about 0.8 kg of body weight on the low-fat diet with about 0.5 kg of fat loss during the last 15 days of that diet. When the subjects were introduced to the low-carb diet, they experienced rapid additional weight loss of about 1.6 kg. BUT most of the weight lost following the transition was as a result of loss of body water because body fat only decreased by 0.2 kg during this period. Overall, over the entire course of the low-carb diet participants lost the same 0.5 kg of body fat. So on both LOW-FAT AND LOW-CARB diets subjects lost the same body fat, not different. They also concluded that since the higher weight loss on the low-carb diet was due to water loss which is not metabolically active, it should not be indicative of a better weight outcome (Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men, Am J Clin Nutr, 2016)

So are these findings indicative of the already known, less appreciated fact that maybe a calorie is a calorie? (a conventional view, that the proportion of carbohydrate to fat in the diet has a physiologically negligible effect on fat loss when dietary protein and energy intake are held constant!). Maybe not so.

In a similar study performed by Dr. Hall on obese men, and this time, obese women, he found that “carbohydrate restriction led to sustained increases in fat oxidation and loss of 53 ± 6 g/day of body fat, whereas although fat oxidation was unchanged by fat restriction, it still lead to 89 ± 6 g/day of fat loss, and was significantly greater than carbohydrate restriction (p = 0.002).” (Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity, Cell Metab, 2015). So do low-fat diets result in greater fat loss? Dr. Hall’s group did not want to answer this monumental question based on just findings from this one study they conducted so they did something bigger…

Following this study Dr. Hall’s group went on to do a meta-study (the study of all studies) to finally end once and for all the low-cab vs low-fat debate. They took data from over 32 controlled feeding studies done in humans and analyzed their body composition and weight loss parameters like they did before for their own studies and concluded “while low-carbohydrate diets have been suggested to partially subvert these processes by increasing energy expenditure and promoting fat loss, our meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure (26 kcal/d; P <.0001) and fat loss (16 g/d; P <.0001) were greater with lower fat diets.” (Obesity energetics: body weight regulation and the effects of diet composition, Gastroenterology, 2017).

So although both low-carbohydrate and low-fat diets cause weight loss when calories are restricted, low-fat diets might cause a greater decrease in body fat content than low-carbohydrate diets after all.

So does that mean we should burn all those sticks of butter at the stake and rejoice? That we should go to the grocery store and pick up every low-fat option of everything we find? The answer is No! Fat intake is just as important for fueling the body as any other macronutrient. Cutting calories and specifically cutting fat intake a little more may help you lose more fat for sure but you do not wanna fall into the trap of cutting fat out completely.  Also, do not rely on fat-free options of processed foods and think you’re gonna lose weight. To replace fats but keep those processed goodies yummy, extra sugar is often added to those foods and that’s not good for any sort of fat or weight loss.

So if you are thinking about starting your own fat loss journey, do a little research, follow an exercise plan, cut some calories moderately (probably more from fat) and get settled on a plan that works for YOU! A plan that you can follow! Remember to be consistent and persistent!

Low-fat diets might have won for now but let’s see what the low-carb proponents come up with next 🙂

Arpit Sharma.

PhD Candidate, Biochemistry.

(reach me at arpitsharmajiit@gmail.com if you wanna feature this post on your blog, blog aggregator website or any another platform)

(Pasta vs Bacon image from: http://www.everydayhealth.com/columns/johannah-sakimura-nutrition-sleuth/low-carb-vs-low-fat-for-weight-loss/)

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