Finally – death to the idea that carbs make you fat?


cerealUS scientist Dr Kevin Hall is keen to kill off the carb-insulin hypothesis of obesity. That’s the one that says carbohydrates, especially refined carbs and sugar, are the primary cause of obesity because they increase circulating insulin. 

Hall, a researcher in the US National Institute of Health’s National Institute of Diabetes and Digestive and Kidney Diseases, has done research in the past hinting at the mortal wounding of the hypothesis. At the International Obesity Congress in Vancouver, Canada, in May, Hall predicted his upcoming research would deliver the fatal blow. That prompted an irritated response from Dr Michael Eades, a US-based world authority on the carb-insulin hypothesis. Eades said Hall was probably ‘going rogue’, and had misrepresented his own data for his own ends.

Hall’s study has just been published in the American Journal of Clinical Nutrition.  It has similarly infuriated another international expert on the carb-insulin hypothesis, Canadian nephrologist Dr Jason Fung. Read on to find out why Fung says Hall’s ‘blatantly biased reporting’ is not the end of the carb-insulin hypothesis. Rather it is the ‘final gasp of the dying paradigm that all calories are equal’. – Marika Sboros

By Jason Fung*

Kevin Hall, the senior National Institutes of Health researcher, recently published a paper in the American Journal of Clinical Nutrition that has received a lot of media attention. This study, he claims, refutes the insulin hypothesis so completely that it is now “dead”.

Jason Fung
Dr Jason Fung

That’s interesting, I thought, as I sat down to read the article.

It was a little surprising, therefore, to read this paper and realize that Hall’s conclusions were entirely his own opinion. He suffers so badly from confirmation bias that he may as well have written: “My mind is already made up regarding the insulin hypothesis. Please do not confuse me with facts.”

Confirmation bias is a well-known psychological phenomenon whereby you accept facts that agree with your pre-formed opinion as true and ignore those that don’t. All facts become filtered through this bias to confirm your previously held opinion. It’s also known as a closed mind.

This happens far more frequently than is often realized or admitted. A similar situation exists in the research behind the weight-losing effect of breakfast.

Researchers used this question of the proposed effect of breakfast on obesity (PEBO) to look at how researchers consistently interpret results depending upon their beliefs.

If you believed breakfast made you lose weight, then studies were interpreted to support this view even if it did not.

BREAKFAST.Two specific tactics are used here: research lacking probative value (RLPV – association data that can’t prove anything) and biased research reporting (BRR). As more people believe something to be true, the effect becomes worse, since all research is now interpreted to fit the preconceived facts.

Starting with the preconceived notion of “A”, all research is interpreted to support this belief (B), and all negative studies are ignored (C). This only reinforces the belief (D), which then leads to biased research reporting. This, of course, is a vicious cycle. The same effect is obvious in CICO (Calories In, Calories Out) diehards.

So, let’s take a closer look at  Hall’s paper and its claims. The paper is titled Energy expenditure and body composition changes after an isocaloric ketogenic diet in overweight and obese men.

Let me give you some background. The award winning science journalist Gary Taubes believes that obesity is essentially a disease of too much insulin – hyperinsulinemia. Since refined carbohydrates stimulate insulin more than fat or protein, reducing said carbs will result in greater fat loss.

He set up the non-profit organization NuSi to raise money to fund research. This paper is the first one published. In it, 17 overweight men were admitted to a metabolic ward where all the food they ate was carefully measured. There was a four-week run-in phase to establish a baseline where men would eat a high-carbohydrate, high-sugar diet, and then switch to a carefully designed low-carbohydrate, low-sugar diet.

Various measurements were then taken, including energy expenditure (EE – how many calories the body is burning), over the next 4 weeks. The basic question is: does a ketogenic diet (KD) cause fat loss?

Here’s the result: Over the four- week KD, yes there was fat loss. There was an initial period of greater weight loss, which all agree may be some diuresis. We can also agree that insulin levels were brought down by the KD. Secondly, using measures of EE there was an increase in calories burnt.

Those are all facts, not opinions, derived straight from the study. Isn’t that a good result?

Dr Kevin Hall
Dr Kevin Hall

Well, if you’re Kevin Hall, no. You need to find a way to spin this in a negative way. Then you can tell all your friends in the media, so you can declare:  “I was right.”

Let’s see how this was done:

When patients embarked on their run-in phase, they were switched to a 2700 calorie/day high-sugar, high-carb diet. This is meant to replicate the Standard American Diet (SAD) that caused the obesity epidemic. Nobody actually believes that this is a healthy diet. Nobody believes it should cause fat loss. But it did. Why?

Anybody who has done research knows why. It’s the effect of going into a study and knowing that people are testing you. It’s a universal effect. That’s the precise reason why we have run-in phases: to establish a proper study baseline when people know they are being watched.

So, people lost weight on this SAD diet. But instead of using this new baseline, Hall decides that the downward trend is the new baseline. The unspoken premise or assumption is that if these people had taken another four weeks of the SAD, they would continue to lose weight at the same rate indefinitely.

WHAT? Are you out of your mind? That’s illogical.

Let’s take an analogous situation. Suppose we are teaching math. We teach a semester with no tests, no exams, no checking of homework and no projects. Students are just supposed to spend one hour in class and do one  hour of homework a day. They all say they do it. Then, unbeknown to them, we test them on a standardized test. They do really badly and score 65%.

Next semester, we have daily tests, a final exam, and daily checking of homework. They still spend one hour in class and one hour on homework. Scores should be theoretically unchanged, because they were doing the same amount of work. Of course, in reality, this is completely false. Because they know we are regularly checking them, they do a better job. Now they score 80%

This is the same effect we see when people enter a study. No matter what we are measuring, things improve simply by entering a study. It happens with blood pressure, blood sugars, cholesterol, diets, depression – everything. But the results do not get better indefinitely. It’s a one time benefit.


Students’  score might improve from 65% to 80% in one semester. This does not mean that another semester of testing will raise their scores to 95%. Instead, they will likely stay at 80%. But this is exactly what Hall does – he assumes this one-time benefit will persist indefinitely.

By making this assumption that the SAD diet will continue to cause fat loss (which logic tells us is false) you can make a positive result negative. So, yes, KD does cause fat loss, but does not increase fat loss and then you can make this your conclusion.

Since most of Hall’s journalist friends never read the paper and only the abstract, it’s easy to convince them.

According to Hall’s assumption, you should therefore simply continue eating the SAD with 25% sugar and expect to lose weight indefinitely. Go ahead. See what happens. I already know. So do you.

You’ll get fat, you’ll get type 2 diabetes, and then eventually, I’ll put you on dialysis and chop off your feet when they go gangrenous. But at least Hall can say he was right.

The second major issue is regarding EE. When you switch from the baseline diet to the KD, the number of calories stays the same. If it causes continued weight loss, then you might expect to see an increase in EE in order for the body to lose weight.

This is called a metabolic advantage. Surprise, surprise – that’s exactly what happened. So how can you spin this one? With language.

Look at how Hall describes the absolutely critical increase in EE.

Here’s what he writes: “The KD coincided with increased EE chamber (57 ± 13 kcal/d, P = 0.0004) and SEE (89 ± 14 kcal/d, P < 0.0001)” (emphasis mine). Hall is telling you that this was merely a coincidence that patients are all burning an extra 57 calories per day. WTF?

There is nothing coincidental about it. You switched them to a KD. EE increased. The P value of 0.0004 means that there is a 99.96% chance that this is NOT COINCIDENCE. Hall knows this as well as I do. This is basic statistics 101.

Hall, a mathematician is surely aware of this.


Hall is saying: “Oh, we switched their diet to test if EE would increase. It really was just a huge coincidence that all 17 men simultaneously increased their EE altogether at exactly the moment we thought it would. Ignore this, guys. Just write your newspaper article about how this proves it didn’t happen.”

So EE increased and yes, the effect waned over time. What did he expect? That things would continue indefinitely in a straight line?  Life doesn’t work that way.

Hall  assumed this would happen for fat loss during the SAD, but then correctly points out that EE does not. If it doesn’t in either case, dude, get a clue.

The reason why EE is so critically important is that this is the key to lasting weight loss. Hall had just been profiled in the New York Times cover page measuring the EE of Biggest Loser Contestants. The reason they all regained their weight was that their EE slowed to such a degree that caloric reduction could not keep up.

So, an intervention like a ketogenic diet that increases EE is HUGE, GREAT NEWS. Except, of course if you’re Kevin Hall, because it means you were wrong. And you care more about your reputation than people’s health and well-being.

EE.Dr David Ludwig, a researcher from a little place called Harvard had shown exactly this same thing in his study from 2012. This study also tested for difference in energy expenditure following different dietary strategies.

Once again, as Hall had shown, the EE is best with a very low carbohydrate diet. So Hall’s study merely confirmed what had already been known.

Some people have also noted that this study controlled calories. So it negates one of the KD’s biggest advantages, which is that it makes you feel full. Well, sorry, guys, that’s not the question it is designed to answer.

Same goes for the fact that there are only 17 people in it. Again, that’s the study design, so it is what it is, and there’s no use complaining about it.

In the end, the main problem is not the study data. The data are excellent. The problem is the “spin”.

Here’s the conclusion Hall writes in the abstract’s conclusion (which is the single most important few sentences of the paper, the one that everybody reads):

Spin.I’ve highlighted what is fact. I’ve crossed out what is pure spin. Did the KD cause body fat loss? Yes it did. And that’s really, really important.

Hall spins this positive into a negative by moving the goalposts:  “Oh but it didn’t do better than before. People eating a 25% sugar diet will continue to lose fat indefinitely at the same rate”.

Umm… What planet are you from, Kevin Hall?

Then he says the increase in EE is “relatively small”. So what? Did it increase or not?

In fact, your own study from the Biggest Loser suggests that weight loss from constant calorie reduction will DECREASE EE, so even the stabilization (let alone the increase) of EE is critically important.

That’s the gold medal, buddy! You just threw it in the garbage.

Hall then downplays this relationship by calling it an “association”. As if the change in EE just happened to occur at the same time as the change in diet. What a load of crap.

You changed the diet and measured the change in EE. Nobody doubts that. It’s causation, pure and simple. So why try to spin this as an “association’” which is a mere “coincidence”? Pure spin.

Hall then further tries to downplay the importance of stable EE by saying it’s ‘near the limits of detection with the use of state-of-the-art technology’. So what? Who cares? Did it stabilize or not? Isn’t that great news? Did you not just show that weight loss efforts fail because of decreased EE?

Unfortunately, spin-doctor Hall is now entering a logic free zone, and many journalists and bloggers are happy to take what is shared at face value. “In this first Biggest Loser study, I demonstrate why stable EE is the most critical factor for weight loss. In this second study I’ll show how stable EE is absolutely worthless. Ta Da!” Hall wants desperately to save his own reputation, even if he has to sacrifice your health to do so. Sad. So sad.

The facts alone, without any spin would be this: A ketogenic diet, independent of calories causes fat loss and causes an increase (or at least the stabilization) in EE. That’s the fact. And I love it. Because I can use that  fact to help heal patients and save lives. Luckily, I can see Clueless Kevin Hall’s blatantly biased reporting for what it is – the final gasp of the dying paradigm that all calories are equal.

Hall and the other study authors  responded saying: “Serious scientific criticisms of the study or its interpretation should be expressed in a letter to the editor of the American Journal of Clinical Nutrition and the study investigators as a whole can respond appropriately.

  • *This blog first appeared on Intensive Dietary Management and is republished with permission.
  • Toronto-based Dr Jason Fung has developed the Intensive Dietary Management (IDM) Program that focuses on treating our generation’s great epidemic – metabolic syndrome. This is a spectrum of disease including obesity, diabetes, high blood pressure, high cholesterol, fatty liver, Alzheimer’s disease and cancer. Dr Fung says diabetes puts people further at risk for heart disease, stroke, peripheral vascular disease (PVD) including amputation, blindness, kidney disease and more.



  1. Thanks Dr. Fung. As a layperson, it’s not always easy to follow the science (at least not quickly). You always do a marvelous job explaining the concepts of a lchf/Kd to the average person. I have the added dimension of putting these into practice over the last 6 years. I have lost and maintained a 32kg loss over that time (w/ relative ease). Nothing like the struggle I endured with SAD diets over the first 3 decades of my life. At 42, I look and feel like I’m 22. Not to mention the increased performance and mental focus I have consistently while eating keto or fasting. May sound corny, but I feel as if I’ve evolved as s person. It only seems to get better as time goes by.

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