Humans – the perfect hybrid machine

Long before the ‘hybrid car” there was the human body – a hybrid ‘machine’ perfectly designed to use either carbohydrates or fat for energy. Like a hybrid car, we can run on one fuel source or the other at any one time.

If we are eating a largely carbohydrate based diet, we will be in ‘carbohydrate mode’ by default. Carb-based foods will be broken down by our bodies to simple sugars and the glucose used to maintain our blood sugar levels. Our liver and muscle glycogen will be topped up, then the rest will be shuttled off to the liver where it will be converted into LDL cholesterol and triglycerides and stored in fat cells.

Historically, in times of plenty, we’d store up glycogen and fat and in lean times, we’d use up our glycogen and then switch fuel sources to be in “fat-burning mode” — accessing our own fat stores, for energy.

The problem is now that we rarely, if ever access our stored fat because we keep eating a carb-based diet.  So we keep getting fatter and fatter.


When we are in “carb burning mode”, the carbs we eat are broken down by different enzymes in our digestive system to their simplest sugar form (monosaccharides) such as glucose, fructose and galactose.

Glucose is the sugar in our blood, so starchy foods such as bread and pasta and potatoes are broken down quickly so they are available to maintain our blood sugar levels.

Monosaccharides are the building blocks of more complex sugars such as disaccharides, including sucrose (table sugar) and lactose (the sugar found in milk), as well as polysaccharides (such as cellulose and starch). When we drink milk for example, the galactose found in it is broken down into lactose and glucose.  When we eat something sweetened with ‘sugar’ (sucrose), it is quickly broken down to glucose and fructose.

Any glucose that is needed to maintain our blood sugar level is used immediately for that purpose and the remainder is used to “top up” our glycogen stores in our muscle and liver. There are only ~ 2000 calories of glycogen – enough energy to last most people one day, so when our glycogen stores are full, excess energy from what we eat is converted to fat in the liver and stored in adipocytes (fat cells).

One problem is that our diets are high in fructose – naturally found in fruit but also as high fructose corn syrup in many processed foods. Fructose can’t be used “as is”, so it is brought to the liver.  If our blood sugar is low, it will be used to make glucose for the blood (via gluconeogenesis) otherwise it will be converted into LDL cholesterol and triglycerides and stored as fat.

Feasting and Fasting

When we don’t eat for a while, such as would have occurred when our ancestors were hunter-gatherers, we’d use up our glycogen stores hunting for an animal to eat, or gathering other edible foods and if we weren’t successful at finding food to eat, then our bodies would access our fat stores, for energy.  This is known as lipolysis. This process is regulated mainly by a hormone called glucagon, but other hormone such as epinephrine (the “fright and flight” hormone), cortisol (the “stress hormone”) as well as a few others (ACTH, growth hormone, and thyroxine) also play a role.

In times of plenty, we’d store up glycogen and fat and in lean times, we’d use up our glycogen, switch into “fat-burning mode” and then rely on our stored fat for energy.

The problem for most of us in North America and Europe is that we have access to food in our homes, in stores and at fast food restaurants 24/7. We can’t go for a walk without passing places selling or serving food and if the weather is bad or we are too tired, food is just a phone call or web-click away. So we just keep storing up our fat for ‘lean times’ that never come.

In addition, irrespective of our cultural background, our eating style is carb based; pasta, pizza, sushi, curry and rice or naan, potato, pita – you name it.  Every meal has bread or cereal grains, pasta, rice or potatoes – and even what we consider “healthy foods” such as fruit and milk have the same number of carbs per serving as bread, cereal, pasta, rice and potatoes. That wasn’t always so. Our indigenous cultural foods were very different.

Compounding that, many “low-fat” products have added sugar (sucrose) in order to compensate for changes in taste from reducing naturally occurring fat, which then adds to excess carb intake.  Sucrose (ordinary table sugar) is made up of half fructose, so a diet high in sugar adds even more fructose transport to the liver, for conversion to cholesterol and fat.

The vilification of fat

In 1977, both the Canadian and US food guides changed in response to the promoted belief that eating diets high in saturated fat led to heart disease. Multiple studies and reanalysis of the data of older studies indicates that saturated fat is not the problem, but that diets high in carbohydrate combined with chronic inflammation and stress, is.

In 2016, it came to light that the sugar industry funded the research in the 1960’s that downplayed the risks of sugar in the diet as being related to heart disease and highlighted the hazards of fat instead – with the results having been published in the New England Journal of Medicine in 1967 with no disclosure of the sugar industry funding*. The publication suggested that cutting fat out of the American diet was the best way to address coronary heart disease, and which resulted in the average American and Canadian as inadvertent subjects in an public health experiment gone terribly wrong. Overweight and obesity has risen exponentially and with that Diabetes, hypertension (high blood pressure) and high cholesterol.

*(Kearns CE, Schmidt LA, Glantz SA. Sugar Industry and Coronary Heart Disease Research A Historical Analysis of Internal Industry Documents. JAMA Intern Med. 2016;176(11):1680-1685. doi:10.1001/jamainternmed. 2016. 5394).

Over the last 40 years the promotion of “low fat eating” by governments and the food industry has resulted in carbohydrate-intake skyrocketing. Every high-carb meal is followed by another high-carb meal, and if we can’t wait, a snack, too. We eat every 2-3 hours, and eating carb-based foods every 2 or 3 hours all day, every day is quite literally killing us.

How do we get fat out of “storage”?

The “key” to unlocking our fat stores, is decreasing overall intake of carbohydrates by decreasing the amount of carbohydrates we eat, both by eating much less of it and on occasion, by delaying the amount of time between meals.

Decreasing carb intake lowers insulin, the fat-storage hormone. At first our bodies access liver and muscle glycogen for energy, but since that is only about a one day’s supply, our bodies then turn to our own fat stores as a supply of energy.

By eating a diet rich in fat and keeping protein at the level needed by the body but not in excess, dietary protein is not used to synthesize glucose, but fat is.

An added bonus is that since insulin also plays a role in appetite, as insulin falls, appetite decreases.

This is the role of a low carb high healthy fat diet, a topic covered in this article.

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To your health!


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