Fat burns in the fire of carbohydrates

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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n 2004, the World Health Organization developed a global strategy on diet, physical activity and health. This strategy was adopted in order to reduce the risk factors responsible the major non-communicable diseases, including diabetes and cardiovascular disease due to obesity (1). The main outcomes of this strategy were the promotion of a healthy diet and the recommendation to reduce the overall consumption of some carbohydrates like sugars and rapidly digested starches (2). Since the implementation of this strategy, a number of research bodies have studied the effects of a low carbohydrate diet on weight loss and more specifically, the metabolic changes that take place when the macronutrient composition of the diet is altered (3).  In order to understand these findings and the overall effects on low carbohydrate diets designed for weight loss, the rules of macronutrient metabolism must be understood… especially carbohydrates.

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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arbohydrates are an important macronutrient for energy production and although the absorbable units produced by fat digestion, Fatty acids and Monoglycerides, can be utilized by the some of body’s cells, there are some processes that can only be carried out using glucose. Brain cells, nerve cells and developing red blood cells can only continue to proliferate in the presence of glucose as a fuel source. During periods of glucose and glycogen depletion (low-carbohydrate diets) the body begins to source glucose by dismantling body proteins. This complicated process is called gluconeogenesis and becomes the continued source of glucose for the body until adequate dietary carbohydrates are returned (6). Continued dismantling of body proteins to produce glucose for energy is not ideal and can impact on the physiological role the absorbable units of proteins, amino acids, provide the body (7). Given the complicated processes of macronutrient metabolism and the differing roles of carbohydrates, fats and proteins, it is clear that altering the nutrient composition of ones diet will have a significant physiological impact on the body.

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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urrent research compiled by Archeson (2010), now shows that manipulating fuel sources in energy production for the purposes of weight loss can be done without the presence of carbohydrates and that in the short term, VLCKD or LCKD acutely induce a number of favorable effects for the dieter, including, rapid weight loss, reduction of circulating triglyceride levels and improved blood pressure. A down side to VLCKD or LCKD’s for weight loss is the number of less desirable physiological effects including, loss of lean body mass, increased loss of calcium through urine and increased levels of plasma homocysteine and low-density lipoprotein-cholesterol, potentially increasing the risk of a cardiovascular event. In addition to this, Last & Wilson (2006) review the difference in weight loss between low carbohydrate and low-fat-higher-carbohydrate diets. They conclude that in the short term, i.e. up to 6 months, greater weight loss occurred with the low carbohydrate diets. Over a 1-year period, however, weight loss did not significantly differ between low carbohydrate and the low-fat-higher-carbohydrate diets. The implications of the above findings, question the long-term impacts of diets, which focus on or restrict any one particular macronutrient group.

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