The War of the Diets – Low-Carb or Low-Fat

There is an ongoing war in the world of diet and nutrition. I call it the war of the diets. This war started many years ago and there just appears to be no end to it. Both sites are blaming each other for a huge number of casualties. Like in so many wars before, it is unlikely that there will be a winner. Books are published, articles written, videos and web pages flourish. Everybody’s expected to choose a side. 


Approximately three decades ago public health authorities decided that we should limit the amount of fat in our diet, primarily saturated fat, as it raises blood cholesterol and increases the risk of heart disease. The McGovern Committee’s report, “Dietary Goals for The United States” was published in 1977. Although possibly not based on solid scientific data, the committee’s main results were confirmed a few years later by the USDA. The main conclusion was that Americans should “avoid too much fat, saturated fat and cholesterol”.

Soon, the demonization of fat, primarily saturated fat, spread around the globe. Public health authorities in Scandinavia and the rest of Europe based their recommendation on the same arguments as the USDA. Although possibly a misinterpretation or oversimplification of the available evidence, in a few years time this led to something we could call the “low-fat mania”. The war of the diets had started. Food manufacturers began providing us with low-fat varieties of almost every food alternative we know. But, fat is difficult to replace, because it is commonly an essential component of good and tasty food. Instead of fat, different types of refined simple sugars, such as the famous high fructose corn syrup were used to make people like the fat-free varieties. The low-carb, low-fat controversy had risen to new heights. Carbohydrates were on the attack, fats were retreating.

As the years went by it became apparent that obesity was on the rise. People were getting fatter and fatter, despite all the low-fat food. Furthermore, type 2 diabetes seemed to be skyrocketing. Was it because we were not following the public health guidelines or was it because of the guidelines themselves? Or is it something completely different? What about inflammation, drugs and harmful chemicals in the environment. No wonder detox is becoming so popular.

Is it possible that the public authorities were wrong? Is it sensible to make general recommendations on diet and nutrition that applies for everybody? Should the obese, sedentary, middle-aged male follow the same diet recommendation as the thirty years younger normal weight, well-trained university student?

Furthermore, research and experience was starting to show that one of the most effective way for an obese or overweight person to lose weight was to cut down on carbohydrates and increase fat consumption. This concept was but forward by Dr. Robert Atkins in his book, The Atkins Diet Revolution, published 1972. Although severely criticized by the scientific and medical community at that time, the low carbohydrate, high fat (LCHF) concepts have survived and are still going strong. The LCHF supporters blame the “low-fat mania”, induced by public health recommendations for the current obesity epidemic which they say is all down to over consumption of sugars and carbohydrates. They are gaining more and more followers and some say the war of the diets may be turning.

One of the biggest culprits of the ongoing war is the concept that a calorie is a calorie. If you eat more than you burn, you will gain weight, if you burn more than you eat you will lose weight. If this is true, the cause of obesity is quite simply that people eat too much and exercise too little. The cure for obesity would also be very simple; eat less and exercise more.

However, there is a lot of evidence indicating that it is not all about calories. Some recent studies have indicated that weight loss seems to be greater on a low-carb diet than on a conventional low-fat diet that has the same number of calories. However, this is not true for all studies. Different macronutrients may possibly have different effects depending on individual factors, such as stature, body weight, age, metabolism, insulin resistance and level of physical exercise.


The cells of our body need a constant supply of energy in order to be able to function normally. This fuel is provided by the so-called macronutrients; carbohydrates, fat and protein. Carbohydrates are a very important source of energy for the human body. In some parts of the world, more than 80% of the energy consumed comes from carbohydrates. Public health authorities today recommend that 45 – 65% of our energy consumption should be provided by carbohydrates.

Before I go further, let’s clarify a few issues. How do we classify carbohydrates? Which carbohydrates are defined as sugars?

Carbohydrates are compounds that contain carbon, hydrogen and oxygen. They are generally classified as monosaccharides, disaccharides and polyscaccharadies. Saccharide means sugar, mono means one, di means two and poly means many. A monosaccharide contains one sugar molecule, a disaccharide contains two sugar molecules and a polysaccharide contains many sugar molecules.

Monoscaccharides and disaccharides are commonly termed sugars or simple carbohydrates, while polysaccharides are usually termed complex carbohydrates or starches. Cellulose and other fibers are also carbohydrates, but they do not provide energy as the body does not possess the enzymes necessary to digest them. Cellulose is commonly found in starchy foods, and although it does not provide energy, it contains vitamins, minerals and other nutrients. This is one of the reasons fiber is considered a healthy food choise. Sugar, however, provides only energy and does not contain vitamins, mineral or fiber.

The three monosaccharides found in food are glucose, fructose and galactose. Fructose is the one most commonly used as a food additive. It is the sugar molecule that has the sweetest taste. High-fructose corn-syrup is commonly added to foods when they are processed.

Three disaccharides are frequently used in food as well; sucrose, lactose and maltose. Sucrose is the typical, white table sugar and contains one molecule of glucose and one molecule of fructose. Sucrose is added to many processed foods.

Glucose and fructose may indeed work very differently for the human body. Glucose is metabolized by every organ in the body. It is our cells most important source of energy. If we don’t get glucose through our diet, our body makes it by a process called gluconeogenesis. Fructose is different as it can only be metabolized in the liver. Depending on our body’s need for energy, fructose will be metabolized to glucose, although this has been debated by some. However, if our energy needs are already met, which is often the case, fructose will be metabolized to fat.

By eating modern diet, rich in added fructose, we may indeed be overloading our liver. Much of the fructose delivered to the liver will be metabolized to fat. Through different complex mechanisms, over consumption of sugar, primarily fructose, may contribute to obesity and the metabolic syndrome as well as many other modern-day diseases like high blood pressure, cardiovascular disease, cancer and Alzheimer´s disease.

Carbohydrates are classified in different ways. They are often divided into two categories; sugars and starches. Sugars are also known as simple sugars or simple carbohydrates, and starches are referred to as complex carbohydrates. The widespread processing of carbohydrate-containing foods has given rise to some new terms. The term highly “processed” refers to foods that are primarily sugar or products made from grains that have been highly refined and sweetened. Examples of such foods are beverages and sugared cereals. In contrast, whole grains and foods made from them are referred to as minimally processed, fiber containing, or quality carbohydrates.

The Role of Insulin

Carbohydrate is the primary stimulus of insulin release from the pancreas. Insulin is necessary to promote glucose uptake by the cells of the body and to inhibit glucose output from the liver. There is a phenomenon called insulin resistance which is commonly associated with overweight, obesity and the metabolic syndrome. Insulin resistance  implies a diminished response to a given concentration of insulin. When insulin resistance is present, insulin may not be able to deliver its actions when carbohydrates are ingested. Insulin resistance is a precursor to type – 2 diabetes.

As insulin resistance develops, a number of physical and biochemical changes may occur. The liver turns more blood sugar into fat and blood levels of triglycerides rise. Blood pressure may rise above normal and levels of HDL cholesterol (the good cholesterol) may go down. Weight gain usually occurs, particularly around the center of the body. This situation may harbor inflammation. Inflammation has been associated with high levels of insulin, type – 2 diabetes and increased risk of cardiovascular disease. Studies have shown that low carbohydrate diets may promote weight loss and metabolic advantages among individuals with insulin resistance.

The Metabolic Syndrome

Approximately 30 percent of individuals in the United States have the so-called metabolic syndrome. The syndrome is defined as three of the following

  • Waist circumference > 102 cm (40 inches) in men and > 89 cm (35 inches) in women
  • Fasting triglycerides > 1.7 mmol/L (150 mg/dL)
  • HDL – cholesterol < 1.0 mmol/L (40 mg/dL) in men and < 1.3 mmol/L (50 mg/dL) in women
  • Blood pressure > 130/85 mm Hg or the use of blood pressure medication
  • Fasting glucose (blood sugar) > 6.1 mmol/L (110 mg/dL) or the use of diabetes medication

These derangements in combination increase the risk of cardiovascular disease. Insulin resistance appears to play a central role in the metabolic syndrome. Although avoidance of saturated fat is a primary target in the public health recommendations, it is likely that low carbohydrate diets may be much more effective among individuals who suffer from the metabolic syndrome.


Physiologically fats are long chains of carbohydrate molecules. The predominant fats in foods and in the body are triglycerides which are made up of three fatty acids attached to a glycerol molecule. Sterols, such as cholesterol and phospholipids, phosphate containing fats are also common. These fats compose the category known as lipids.

Fatty acids are chains of carbon and hydrogen, ending with a so-called carboxyl group. The lengths of the fatty acid chain vary from 4 to 24 carbons. The term saturated implies that no more hydrogen atoms can be incorporated into the molecule. The term unsaturated means that there is room for more hydrogen atoms, monounsaturated meaning that there is room for one such atom and polyunsaturated meaning that there is room for more than one atoms. Although so-called trans fatty acids may be found in small amounts in nature, they are usually produced synthetically by partial hydrogenation of polyunsaturated fatty acids. This is done in commercial food processing to make liquid oils more solid and to increase the shelf life of the product. A number of studies indicate that trans fatty acids negatively influence cardiovascular risk.

Two 18 carbons fatty acids are essential fatty acids – linoleic (omega-6) and alpha – linolenic acid (omega-3). The body cannot manufacture these fatty acids, so they must be consumed in the diet. Fortunately, those two essential fatty acid are widely found in food.

From a health perspective, there are certain fats that have been emphasized, because of the proposed effect on the risk of cardiovascular disease. Unsaturated fatty acids such as omega – 3 fatty acids are considered healthy options. Conversely it has been recommended that the consumption of saturated fatty acids be limited and that trans fatty acid consumption be as low as possible due to detrimental effect on the risk of cardiovascular disease.

Usually fats in food are a combination of saturated, monounsaturated and polyunsaturated fatty acids. We commonly tend to identify fat in the food based on the type of fatty acid that is predominant. We know that butter and steak for example predominantly contain saturated fatty acids and olive oil for example contains mainly unsaturated fatty acids.

The polyunsaturated omega – 6 and omega – 3 fatty acids are building blocks for the so-called prostaglandins. The prostaglandins play an important role for inflammation in the human body. The omega-3’s are building blocks for anti-inflammatory prostaglandins and the omega-6’s are building block for inflammatory ones. Both these fatty acids therefore play an important role. However, it has been suggested that the overabundance of omega-6 in the western diet compared to omega-3 may be undesirable.

Some studies indicate that consumption of saturated fats may increase blood levels of LDL – cholesterol (the bad cholesterol).  There is an association between blood levels of LDL- cholesterol and the risk of cardiovascular disease. Some studies have indicated that replacing saturated fatty acids with polyunsaturated may decrease the risk of heart disease. However, there is indeed very weak scientific evidence linking saturated fat with increased risk for cardiovascular disease.

What Is a Low Carbohydrate Diet?

For general health, public health authorities recommend that carbohydrate intake should be 45 – 65 percent of total energy intake. Let’s look at what this means. An adult woman who engages in daily walking activity may need an estimated 2.000 kcal per day. A recommendation that carbohydrate be 45 – 65 percent of total energy implies that 225 to 325 grams of carbohydrates should be consumed daily.

There is no readily available definition of what “low carb” means. In the first stage of the Atkins diet the upper limit of carbohydrate consumption is 20 grams daily. However, in later phases, carbohydrate consumption is increased. I guess that every diet that recommends less than 100 grams of carbohydrates a day will have to be considered a “low carb” diet.

Most low carbohydrate diets recommend increased consumption of fat in order to meet the body’s requirements for energy.

The War of the Diets

The Hundred Years War is thought to be the longest single war in history, it lasted 116 years. It consisted of a series of battles between England and France, beginning in 1337 and ending in 1453. It began when King Edward III of England invaded France, claiming the throne of France for himself. His successors kept the fight going. Shakespeare admirers will know that Henry V defeated the French at the Battle of Agincourt in 1415.  Joan of Arc led the French to several successes in 1429. Paris was finally liberated from English rule in 1436, and the French finally sent the English out of France completely in 1453.

I don´t know whether the War of the Diets will last for more than hundred years or if there will be a Joan of Arc type dietitian or physician that will come to the rescue, only time will tell. However, I guess that a scientific or a theoretical war may actually have some positives. It certainly provokes lively debates and it may actually stimulate scientific research. The downside is that if you have already chosen a side, you run the risk of neglecting, or not choosing to accept scientific results or arguments that don´t support your own opinion. This may cause argumentation that should be based on scientific data and reasoning to take on the form of propaganda. Unfortunately, we see this happening all the time.

Maybe carbohydrates are not bad as such and maybe fat is not bad either. It may indeed be that when you put those two together that problems start to occur. Maybe moderation is the key as so often is the case.

Some of the “low carb” spokesmen have made the headlines recently. The work and writings of Gary Taubes, Robert H. Lustig, Jonny Bowden, Jeff S. Volek, Stephen D Phinney and Andreas Eenfeldt has surely helped us to better understand the mechanism behind obesity and the metabolic syndrome. It has certainly opened our eyes to the fact that fat is not a problem in our diet today. However, the low-carb supporters have to be careful. If their argumentation is not based on real science and takes the form of propaganda, the cause will be damaged.

Recently a retired thoracic surgeon made the international news headlines by “speaking out on the real cause of heart disease”. This media coverage did certainly not help the low-carb cause although it was meant to do so. Recently I wrote an article explaining why I did not like the surgeons opinionated, nonscientific approach to this important issue.

Recently the UCSF introduced a very interesting video series called “The Skinny on Obesity” where Dr. Robert H. Lustig plays a key role. Keep in mind that if Dr. Lustig is a soldier participating in the War of the Diets, this could be a propaganda film. But, I like it anyway and I think everybody should watch it.  Dr. Lustig is on a crusade against the junk food industry and he has my full support. The videos are professional, informative and fun to watch. I look forward to see more episodes.

A few final words on the war of the diets. Low carb or low fat. Who will prevail?. I am a clinician. I am not going to choose sides in the War of the Diets. I don’t have to. I will take what is best from both sides. I will use scientific data to guide my way to choose what is best for my patients. But, I guess I am allowed to some opinion. Here it is:

  • I doubt that generalized diet recommendations can be given that apply to everybody
  • Over consumption of fat is a rare problem nowadays
  • Saturated fatty acids are not dangerous for our health
  • If your primary target is lowering blood levels of LDL cholesterol (the bad cholesterol) you may benefit from reducing the consumption of saturated fat
  • Mono – and polyunsaturated fats may be a healthier food choice than saturated fats
  • Over consumption of simple refined sugars may contribute to obesity
  • People who are overweight or obese may not tolerate carbohydrates as well as those who are normal weight
  • Individuals who are overweight or obese are likely to lose weight and improve their metabolic function and well being by reducing carbohydrate consumption and eat more fat
  • Not all carbohydrates are bad
  • Choose complex carbohydrates rich in fiber
  • Avoid simple refined sugars
  • If you are an athlete or exercise a lot, the use of simple carbohydrates can be warranted to provide you with easy access fuel
  • People are different and have different metabolic function. Therefore dietary recommendations should be tailored according to the individual needs.


4 thoughts on “The War of the Diets – Low-Carb or Low-Fat”

  1. Based on seeing Dr. Lustig comment in a number of contexts, I think he’s a soldier, but just not in the low-carb vs. high-carb war. He’s fighting a war against refined sugar and its cousin, HFCS. That such a stance usually results in a lower-carb diet is a byproduct. Initially, Lustig was against low-carb diets per se. When someone explained the details to him, he backtracked, saying that the plan described was “OK.”

    I have always been puzzled that he’s neutral in this regard, since even complex carbohydrates ultimately break down to glucose and stimulate insulin, and a high-carb diet stimulates insulin significantly and often. This sets the stage for insulin resistance and its attendant problems in many people.

  2. I have not been able to find a graph of heart.disease frequency vs cholesterol ( LDL or Total). Since so much of modern medicine ties heart disease risk to cholesterol I find this curious. Does anyone know of such a comparison? What does the Framingham Heart Study show.

  3. Dear Dr Sigurdsson,
    I discovered your blog recently and I am currently in the process of reading all your articles from the beginning (including the comments !). I really appreciate your smart and moderate view on these controversial subljects.
    This article on “the war of diet” is my favorite (up to now…). I am not a doctor nor a dietetician, but I have a scientific background (material science engineer) and I am very interested in the field of nutrition and its impact on medical issues. My daughter just graduated from a medical school in Belgium and started praticing medecine (general practioner) a week ago. I realise how poor knowledge student from medical schools have on that matter, unfortunately. During my self research I hardly find moderate and sound scientifcally based views on the subject… There are exception of course. I find Prof Tim Spector and Prof Christopher Gardner good example in that respect. I don’t know if you had the opportunity to come accross their writings and videos ?
    Your blog is excellent and I really appreciate your critical , scientific and moderate tone.
    Thank you very much to share your views in such an intersting way ! I realize myself how difficult it is to remain unbiased, open minded and humble when one has strong beliefs… Thank you for the lesson.
    Brigitte (from Belgium).

    • Hi Birgitte
      Thank you for the kind words. Appreciate your interest and input. Hope you continue to visit my blog and feel free to share your thoughts.


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