In this post I’m brining you some important information… Specifically, I hope to address a common misconception about low carbohydrate diets designed for weight loss. Hint… removing carbohydrates from your diet isn’t the answer to your weighty worries. Read on to find out why…
-JA
‘Fat burns in the fire of carbohydrates’
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Metabolism is an all-encompassing term that refers to the chemical reactions within cells. The body’s cells metabolize by degrading, synthesizing and transforming the three forms of energy: carbohydrates, fats and proteins. Nutrients absorbed by this process are used by the body to promote normal growth, maintenance and repair. Carbohydrates are the body’s preferred energy-yielding nutrient for producing cellular energy in the form of adenosine tri-phosphate (4). Dietary carbohydrates are digested to form the absorbable unit glucose, which plays a central role in carbohydrate metabolism. In order to maintain the energy needs of the body, dietary carbohydrates must be consumed at frequent intervals. During periods of carbohydrate depletion, the body can maintain homeostasis by releasing the stored form of glucose known as glycogen from muscles and the liver. However, these glycogen stores are limited and once depleted; fats become the fuel for energy. Metabolizing fat for the body’s energy is not a direct substitute for carbohydrate breakdown and in fact, a number of metabolic changes occur. Normally, fat oxidation for energy requires the presence of glucose and the 2 energy fuels are broken down together. This process provides the formation of a fat-glucose complex whereby the combined molecules break down completely. This process of fat metabolism provides the basis for the analogy; fats burn in the fire of carbohydrates. Therefore, fat metabolism for energy, in the absence of glucose becomes complicated. Without glucose to form the fat-glucose complex for breakdown, fat units bind together to form ketone bodies. The continued physiological processes that lead to the formation of ketone bodies can cause a condition known as ketosis, whereby the accumulation of ketone bodies in the blood causes a disruption to the body’s normal acid-base balance (5). Prolonged ketosis can eventually lead to ketoacidosis and an impaired ability of the liver to perform gluconeogenesis. Ketosis is one of the common metabolic changes thought to occur when a low carbohydrate diet is followed (6).
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According to review articles by Westman et al. (2007) and Last & Wilson (2006), low carbohydrate diets restrict caloric intake by reducing the consumption of carbohydrates to 20 to 60 g per day. This in effect, lowers glucose availability and changes insulin and glycogen concentrations, directing the body away from fat storage and toward the metabolic oxidation of fat. Key to defining a diet as low carbohydrate is the presence of measurable ketones in the urine. These diets have been referred to as very-low-carbohydrate ketogenic diet (VLCKD) or a low-carbohydrate-ketogenic diet (LCKD). It is these diets that have a potent effect on metabolic pathways and challenge the traditional school of thought that fat burns in the fuel of carbohydrates.
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For rapid weight loss results, it appears that choosing a diet low in carbohydrates will have an effect. This is likely due to the loss of fluids often associated with stored glycogen and the loss of lean body mass as proteins are broken down for glucose-fuel. In conclusion, it is true that ‘Fats burn in the fuel of carbohydrates’ in the traditional sense of macronutrient metabolism. In the absence of carbohydrates, like we see in low carbohydrate diets, fats are oxidized as a fuel source for the body, but the breakdown is not complete. Ketosis can result from this type of diet and the physiological changes this can have on the body are undesirable, especially loss in liver function. Instead of choosing a diet that may have yet unknown long term effects on the body it may be best to follow the Australian Guide to Healthy Eating and ‘consume a variety of foods across and within the five food groups and avoid foods that contain too much added fat, salt and sugar’ (8).
-JA