The international scientific literature is unanimous in setting the lower limit for the daily caloric intake to 1200 kcal for women and 1500 kcal for men (adults).
To make negative the daily caloric intake, and therefore lose body weight, but expecially lose body fat, evaluation of actual caloric needs of the subject will be alongside:
- the correct distribution of meals during the day;
- an increased physical activity, by which the negative balance can be achieved without major sacrifices during meals.
This will make weight loss easier and protect from subsequent weight gains and yo-yo effect.
Ultimately, there must be a change in lifestyle.
- Body fat and “miracle diets”
- Body fat and reduction of energy intake
- Yo-yo effect
Body fat and “miracle diets”
So, the best strategy for losing body fat is not a drastic reduction in caloric intake, nor follow constrictive or “strange” diets, such as hcg diet plan, sacred heart diet, paleo diet, Master Cleanse diet (the diet that Beyonce did), etc., that require to eliminate or greatly reduce the intake of certain macronutrients, mostly carbohydrates.
Such conducts can be:
- very stressful from psychological point of view;
- not passable for long periods;
- hazardous to health because of inevitable nutrient deficiencies.
Finally, they do not ensure that all the weight lost is only or almost only body fat and are often followed by substantial increases in body weight and/or by yo-yo effect.
Body fat and reduction of energy intake
An excessive reduction of energy intake means eating very little and this determines the risk, high, not to take adequate amounts of the various essential nutrients, that is, what we can’t synthesize, such as vitamins, certain amino acids, some fatty acids and minerals, including e.g. calcium, essential for bone metabolism at every stage of life, or iron, used in many body functions as the transport of oxygen to the tissues. This results in a depression of metabolism and hence a reduction in energy expenditure.
Whether the reduction in energy intake is excessive, or even there are periods of fasting, it adds insult to injury because a proportion of free fatty mass will be lost. How?
Reduction in energy intake and role of carbohydrates
Glucose is the only energy source for red blood cells and some brain areas, while other brain areas can also derive energy from ketone bodies, which are a product of fatty acid metabolism.
At rest, brain extracts 10% of the glucose from the bloodstream, a significant amount, about 75 mg/min., considering that its weight is about 1.5 kg. To maintain a constant glycemia, and thus ensure a constant supply of glucose to tissues, we needs to take carbohydrates or alternatively amino acids, both easily obtained from foods.
In the case of a low or absent dietary intake of carbohydrates, whereas after about 18 hours liver glycogen, which releases glucose into circulation, depletes, body synthesizes de novo glucose from certain amino acids through a process called gluconeogenesis (actually this metabolic pathway is active even after a normal meal but increases its importance in fasting).
But what’s the main source of amino acids in the body when their dietary intake is low or absent? Endogenous proteins, and there is a hierarchy in their use that is before we consume the less important and only after the most important ones. For the first digestive enzymes, pepsin, chymotrypsin, elastase, carboxypeptidase and aminopeptidase (around 35-40 g) will be used; successively liver and pancreas slow down their synthesis activities for export proteins and unused amino acids are directed to gluconeogenesis. It’s clear that these are quite modest reserves of amino acids and it is the muscle that will undertake to provide the required amounts of amino acids that is proteolysis of muscle proteins begins.
Note: Anyway, there is no absolute sequentiality in the degradation of several proteins, there is instead a plot in which, proceeding, some ways lose their importance and others will buy. So, to maintain constant glycemia the protein component of muscle is reduced, including skeletal muscle that is a tissue that represents a fairly good portion of the value of the basal metabolism and that, with exercise, can significantly increase its energy consumption: thus essential for weight loss and subsequent maintenance. It is as if the engine capacity was reduced.
One thing which we don’t think about is that heart is a muscle that may be subject to the same processes seen for skeletal muscle.
Ultimately make glucose from proteins, also food-borne, is like heat up the fire-place burning the furniture of the eighteenth century, amino acids, having available firewood, dietary carbohydrates.
Therefore, an adequate intake of carbohydrates with diet prevents excessive loss of proteins, namely, there is a saving effect of proteins played by carbohydrates.
Mammals, and therefore humans, can’t synthesize glucose from fats.
What goes in when carbohydrates goes out?
The elimination or substantial reduction in carbohydrate intake in the diet results in an increased intake of proteins, lipids, including cholesterol, because it will increase the intake of animal products, one of the main defects in hyperproteic diet.
In the body there are no amino acids reserves, thus they are metabolized and, as a byproduct of their use, ammonia is formed and it’ll be eliminated as toxic. For this reason high-protein diets imply an extra work for liver and kidneys and also for this they are not without potential health risks.
An increased fat intake often results into an increased intake of saturated fatty acids, trans fatty acids, and cholesterol, with all the consequences this may have on cardiovascular health.
What has been said so far should not induce to take large amounts of carbohydrates; this class of macronutrients should represent 55-60% of daily calories, fats 25-30% (primarily extra-virgin olive oil) and the remainder proteins: thus a composition in macronutrient that refers to prudent diet or Mediterranean Diet.
Body fat and the entry in a phase of famine/disease
A excessive reduction in caloric intake is registered by our defense mechanisms as an “entry” in a phase of famine/disease.
The abundance of food is a feature of our time, at least in industrialized countries, while our body evolved over hundreds of thousands of years during which there was no current abundance: so it’s been programmed to try to overcome with minimal damage periods of famine. If caloric intake is drastically reduced it mimics a famine: what body does is to lower consumption, lower the basal metabolism, that is, consumes less and therefore also not eating much we will not get great results. It is as if a machine is lowered the displacement, it’ll consume less (our body burns less body fat).
Yo-yo effect or weight cycling, namely, repeated phases of loss and weight gain, appears related to excess weight and accumulation of fat in the abdomen.
Several studies suggest a link in women with:
- increased blood pressure;
- gallbladder disease;
- significant increase in binge eating disorder;
- a sense of depression with regard to weight.
Lastly, yo-yo effect is related to a greater easy to gain weight than those who are not subject to it. In this regard there should be emphasized that the weight cycling occurs over years, during which, aging, the rate of metabolism inevitably tends to decrease: this could make more difficult the subsequent losses.
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Montani J-P., Viecelli A.K., Prévot A. & Dulloo A.G. Weight cycling during growth and beyond as a risk factor for later cardiovascular diseases: the ‘repeated overshoot’ theory. Int J Obes (Lond) 2006;30:S58-S66. doi:10.1038/sj.ijo.0803520
Ravussin E., Lillioja S., Knowler W.C., Christin L., Freymond D., Abbott W.G.H., Boyce V., Howard B.V., and Bogardus C. Reduced rate of energy expenditure as a risk factor for body-weight gain. N Engl J Med 1988;318:467-472. doi:10.1056/NEJM198802253180802
Sachiko T. St. Jeor S.T. St., Howard B.V., Prewitt T.E., Bovee V., Bazzarre T., Eckel T.H., for the AHA Nutrition Committee. Dietary Protein and Weight Reduction. A Statement for Healthcare Professionals From the Nutrition Committee of the Council on Nutrition, Physical Activity, and Metabolism of the American Heart Association. Circulation 2001;104:1869-1874. doi:10.1161/hc4001.096152