The Carbohydrate-Insulin Hypothesis is Wrong – Hormonal Obesity VI

By Jason Fung, MD

Let’s return to discussing the causes of obesity.  To start with the Hormonal Obesity Part I click here.

Let’s recap.  We’ve explored why the Caloric Reduction as Primary (CRaP) model also known as the calories in, calories out theory is wrong in the Calorie series.  By looking at causal rather than correlation studies, we can see that the hormones insulin and cortisol can both cause obesity.

We can give people insulin and cortisol and they will gain weight.   When we take it away, they will lose the weight.  For the moment we will focus on insulin, since that tends to be the bigger player in obesity.

Once we accept the fact that insulin causes obesity, then we will want to know what caused the increased insulin levels that caused obesity in the first place.  The most obvious candidate is the fattening carbohydrates.  These are the highly refined grains and sugars.

Because these carbohydrates are highly refined, they tend to raise blood sugars and blood insulin levels quickly.  This will tend to cause weight gain and obesity.  This is known as the Carbohydrate-Insulin Hypothesis (CIH), and is the basis of the Atkins diet and many other low carbohydrate (Dukan) and very-low-carbohydrate diets (ketogenic diet).

However, it quickly becomes clear that this hypothesis must be either wrong or incomplete.  The most obvious problem is that of the Asian rice eaters of the 1990′s.  East Asians tend to eat a lot of rice compared to North Americans.  Most of their rice consumption is white rice, which is a refined carbohydrate.

If they are eating so much refined carbohydrates, then you would expect that the Chinese in the 1990′s would be extremely obese.  The problem, of course, was that this was not so.  There were very low obesity rates in East Asia until more recently in the 2000′s when their diet became much more Westernized.  Poor fools.

It is useful to study these historic patterns because many diets have become much more Westernized during this current period of globalization.

Let’s look at this study:
Nutrient intakes of middle-aged men and women in China, Japan, United Kingdom, and United States in the late 1990s: The INTERMAP Study – Journal of Human Hypertension (2003) 17, 623–630 Zhou BF

Using 24-hour dietary recall and 24 hour urine samples they compared the diets of 4 groups of people from the USA, UK, China and Japan.

The total carbohydrate intake in China was far in excess of the other nations.  If the CIH was correct, this would predict that obesity in China would be the highest of the group.  This is not true.

There is clearly something else going on here.  While the total carbohydrate intake was very high, the intake of sugar was very low compared to the rest of the world.  There seems to be something specific to sugar that may be much more obesogenic than other carbohydrates.

Japan is also very interesting.  While total carbohydrate intake is not higher, sugar intake is also lower than either the US or the UK.  Japan also had very low levels of obesity until recently.

There is one other major difference in refined carbohydrate intake.  East Asians tend to take most of their carbohydrates as rice whereas Western societies tend to take their carbohydrate as refined wheat and corn products.

It is possible that rice is less obesogenic than wheat.  There are some who also postulate that wheat that we eat currently is far different from the original wheat that was grown.  One of the New York Times bestsellers is a book called Wheat Belly that suggests this is the major problem.  It is certainly true that 99% of commercially grown wheat is dwarf and semi-dwarf varieties.  The health implications of changing the wheat are unknown, so it remains a very real possibility.

We will unravel the mystery of the 1990′s Thin Chinese Rice Eater in due course.  The answer is far more nuanced than we can cover in this post.  However, what we can say at this point is that the CIH in its current state is not correct.  It is an incomplete theory.

In a similar light, we can point to a multitude of primitive societies that eat predominantly carbohydrate diets.  The Kitavans, for instance, studied by Stefan Lindeberg ate a high carbohydrate diet but had a very low serum insulin and virtually no obesity.  Despite a 70% carbohydrate (unrefined) intake, the Kitavans had serum insulin levels below the 5th percentile of the Swedes.

So, it seems that low insulin levels associates with low obesity rates, it is not at all clear that high carbohydrate intake is the primary cause of high insulin levels.

Similarly, the Okinawans eat plenty of sweet potato (carbohydrate).  Yet they are one of the longest lived peoples in the world and have historically had very little obesity.

The CIH reflects modern medical knowledge circa 1850 when Banting published “A Letter on Corpulence”.  While it is not entirely wrong, it is not entirely right either.  This has led many to abandon this theory rather than try to reconcile it with the known facts.
The link from insulin to obesity seems very solid.  Giving insulin to people causes weight gain and taking it away leads to weight loss.  However, it is the link from carbohydrates to insulin that is incomplete.  There are many things that can lead to increase in insulin, as well as many things that can lead to a decrease in insulin.

The carbohydrate-insulin hypothesis is not so much wrong as incomplete.  The notion that carbohydrates are the only driver of insulin is incorrect.  We need to know what increases and decreases insulin.

In order to develop a more complete understanding of the causes of obesity, we will need to discuss the phenomenon known as insulin resistance.  We will need to look at the importance of meal timing.  We will need to look at the traditional role of fasting.  We will discuss diabetes in detail.

We will need to explore the role of fiber.  We will discuss resistant starch.  We will need to explore the role of vinegar.  We will look at fructose and sugars in more detail.  We will need to look at the role of wheat specifically.

Strap on your seatbelts – we will be taking off shortly.

Continue to Hormonal Obesity Part VII here.
Begin here with Calories I
See the entire lecture – The Aetiology of Obesity 2/6 – The New Science of Diabesity

By The Fasting Method

For many health reasons, losing weight is important. It can improve your blood sugars, blood pressure and metabolic health, lowering your risk of heart disease, stroke and cancer. But it’s not easy. That’s where we can help.

Jason Fung, MD

By Jason Fung, MD

Jason Fung, M.D., is a Toronto-based nephrologist (kidney specialist) and a world leading expert in intermittent fasting and low-carb diets.

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