The FAT In Sugar

 “What if how much you eat and how much you exercise is much less important than WHAT you eat?  What if what nutritionist and dietitians (and thus the doctors they teach) have been wrong for the last 25 years?”

That was the end of my last post.  If you are reading this and you have not read part 1: The FAT In Me, Please do so.  Let’s take a look at what I was getting at.

Three weeks ago a simple dietary question started me on an exploration of the diet world as well as current trends in nutrition.  During the process I came across a lecture from 2008, SUGAR: THE BITTER TRUTH, by Dr. Robert Lustig.  This lecture, along with several follow-up lectures and articles has led to my new nutritional awareness. 

Dr. Lustig is a very well-known and respected physician who is an expert on treating obesity.  In his lecture he presents, in my opinion, near indisputable evidence that the cause of most obesity in this country is in fact SUGAR.  In particular, it is the sugar fructose that he implicates as the white devil.  We know that increased caloric intake leads to obesity and diabetes.  However, Dr. Lustig shows that when the PERCENTAGE OF CALORIES FROM SUGAR goes up but calories remain the same, the correlation to diabetes and obesity because much more pronounced!  Dr. Lustig shows IT'S NOT JUST THE CALORIES, ITS SUGAR CALORIES.

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I am not one to fall for the latest fad research topic so I did my due diligence to both myself and my patients and began to research this topic at length.  I warn you though, it is hard to ignore what Dr. Lustig is getting at given he provides ample scientific proof.  What I found is that most nutritionists now agree with him.

You can probably get more out of watching his lecture than reading my synopsis but I will try to make it a lot easier to understand.  Let’s first explore metabolism.  

Our bodies need fuel to run.  We take in fuel in the form of food and break it down through various processes to form energy.  This “fuel” comes in one of three forms:  FAT, PROTEIN, or CARBOHYDRATES. Let’s take a closer look at each component and the diets based on those components. 

FAT: 

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Dietary fats (triglycerides) are broken down in the gut and converted into fatty acids.  These fatty acids are then further manipulated before going to various tissues of the body.   The cells can then either burn them for fuel or store them as fat. 

Here lies the principle of the low fat diet (ADA, USDA, DASH).  In theory if we take in less fat we will have less fat to store.  Seems sound, but the evidence doesn’t show it.  I have plenty of obese patients that eat low fat diets.  According to research described by Dr. Lustig, the average American has reduced the percentage of fat in their diet by 10% over the last 30 years (From 35% to 25%) yet we continue to get fatter.  Meanwhile the percentage of calories from carbohydrates has continued to rise.

Low fat diets have some flaws.   Fat consumption leads to earlier satiety than protein or carbohydrates and generally foods that are higher in fats tend to taste better as well.  These two principles make low fat diets difficult to stick with.  Also studies show that when people embark on diets that are low in fat, they will replace the missing calories most often with carbohydrates rather than protein either purposely or unintentionally.  We will get to why this is bad in just a little bit.

PROTEIN:

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            Protein metabolism is much simpler to explain although the process is actually rather complex.  When protein is ingested it is broken down through a number of processes into amino acids.  Amino acids can then be used to either directly to form cellular energy or can be converted to glucose in a process called gluconeogenesis.  This process occurs only in very minute amounts unless blood sugar is low.  This is the concept behind the high protein diets (ATKINS, ZONE, SOUTH BEACH).  The super low levels of carbohydrate drive down blood glucose levels which drives your body to look preferentially to protein and fat as energy sources.  In general these “dieting” techniques are actually quite effective but they tend to produce a lot of bad byproducts and they are very hard to stick to long term.

CARBOHYDRATES:

            Carbohydrates are essentially sugars.  They come in many forms but in the end they all get broken down into one of four basic monosaccharaides (sugars).  Since glucose and fructose are far more common than the other two, we will focus on them.  There are not many high carb diets although the ORNISH diet is one that is high in “low glycemic index” carbohydrates while being very low in protein and fat.  The ORNISH diet is also usually calorie restricted and is extremely high in fiber while being relatively lower in fructose.   

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GLUCOSE – Is the essentially sugar on which all animals function.  An example would be the natural sugars found in a slice of bread.  Your body readily consumes glucose as energy.  In fact 80% of the glucose you eat is burned off.  The other 20% is transported to the liver.  During processing of the liver portion, 30% of this will be converted to fat regardless of your activity level.  However a very high activity level could then lead to fat breakdown for increased energy need.

            FRUCTOSE – Fructose is the sugar found naturally in most fruits.  It is also found in High Fructose Corn Syrup (HFCS) and table sugar.  Fructose is much sweeter than glucose.  Your body can not readily use fructose thus 100% of all fructose consumed must be broken down in the liver.  Like glucose, 30% of the liver metabolized portion will be converted to fat. 

Let’s take a look at what I just said via a mathematical example:

Glucose Breakdown (120 calorie sample): 

• 96 calorie burned (80%) à 24 calorie to liver (20%) à 7.2 calorie to FAT (30%)

Sucrose Breakdown (120 calorie sample, 50% fructose): 

• 60 calories glucose à 48 calorie burned à 12 calorie to liver à 3.6 calorie to fat
• 60 calories fructoseà 0 calorie burned à 60 calorie to liver à 18 calorie to fat
• 18 + 3.6 = 21.6 calories to FAT

HFCS (120 calorie sample, 55% fructose): 

• 54 calories fructose à 43 calorie burned à 11 calorie to liver à 3.3 calorie to fat
• 66 calories fructoseà 0 calorie burned à 66 calorie to liver à 20.4 calorie to fat
• 20.4 + 2.1 = 23.7 calories to FAT

WOW!

The math demonstrates Dr. Lustig’s key point; while all calories are in fact calories, they do not all behave the same in the body.   Even more important is the realization that FRUCTOSE is making us fat.  An alarmingly large amount of the fructose you consume is directly converted to fat during processing. 

Sadly, fructose consumption continues to rise.  Early humans consumed around 15 grams of fructose a day, almost all of which was packaged with natural fibers to delay digestion and absorption (This decreases the percentage of the fructose that is converted to fat).  Fructose in the American diet has almostdoubled from 37 grams a day in the 1970’s to well over 60 grams of fructose daily!  

Everything I just wrote boils down to this:  SOME people get fat because they eat too many calories and exercise to little.  However MOST people get fat because they eat the wrong kind of calories.

Check back in another week or so when I following up with part 3 of the series:  The FAT In You!