Essential Reading for Weight Loss: A Detailed Guide to Body Fat Distribution and Key Fat-Loss Principles

Fat Storage:
Where exactly does body fat hide?

Adipose tissue primarily consists of vast numbers of fat cells clustered together. An adult typically possesses around 30 billion fat cells, though some obese individuals harbour over 90 billion.

To elaborate briefly, it is generally understood that fat cells expand and contract in size but remain stable in number after adulthood. Even with weight gain, their quantity does not increase. However, studies indicate that in cases of extreme obesity—where body weight exceeds 70% of the standard weight—such as a woman standing 1.6 metres tall and weighing 190 jin (approximately 95 kg)—not only do fat cells enlarge, but their number also increases. This may occur because existing fat cells expand to their maximum capacity, prompting an increase in cell count.
Thus, when weight gain reaches a certain threshold, both the volume and number of fat cells increase. Conversely, during weight loss, fat cell volume decreases, yet their number remains unchanged. Consequently, if weight is regained through excessive eating, these shrunken fat cells rapidly absorb fat and enlarge once more.

Classic adipose tissue is categorised into white fat (yellow fat) and brown fat.
Why do different types of fat exist? Because bodily fat serves distinct functions: energy storage, thermal insulation, organ separation, and heat production. White fat stores energy, accumulating surplus calories as triglycerides. Thus, when we overeat and become overweight, the stored fat is predominantly white fat. White fat constitutes the predominant form, accounting for over 90% of all adipose tissue. Both subcutaneous and visceral fat fall under this category. Consequently, individuals with prominent beer bellies or significant fat deposits on the thighs and buttocks typically possess higher levels of white fat.

Another type is brown adipose tissue, distributed around the neck, back, and heart. Its primary function is to expend energy. What? Fat expends energy?

Indeed, because this brown fat contains numerous mitochondria, giving it a darker colour. It releases energy produced by oxidising fat through these mitochondria in the form of heat. Thus, brown fat can be likened to skeletal muscle, serving as a major organ for heat production and energy expenditure in the human body. Just 50 grams of activated brown fat can increase daily resting energy expenditure by 5%, equivalent to 75–100 kcal/day. Over a year, this translates to a reduction of 4–4.7 kilograms of fat!
Let us examine fat tissue storage from the body's surface inward.

Fat Fat
First is subcutaneous fat, which accounts for approximately two-thirds of the body's fat reserves. This layer primarily shapes our plump appearance.

Subcutaneous fat's primary function is thermal insulation. Given the human body's lack of body hair, fat's warming properties were crucial for early humans. Its secondary role is energy storage; in many hibernating mammals, subcutaneous fat provides nearly all the energy required to survive winter. Additionally, women generally possess more subcutaneous fat than men, as oestrogen promotes its development. Its functions include energy supply and supporting growth, particularly in young women whose bodies accumulate subcutaneous fat more readily to prepare for pregnancy and childbirth.
Subcutaneous fat garners attention primarily because its accumulation leads to obesity and affects body shape.

Measuring subcutaneous fat thickness can indicate a person's level of adiposity and estimate their overall body fat percentage. Subcutaneous fat thickness is typically measured using calipers, with common sites including the back (scapular region), chest, back of the arms, and beside the navel.

Gently pinch the skin and subcutaneous fat at the measurement site between thumb and forefinger, then use the calipers to record the thickness. Naturally, without calipers, one may directly measure the skinfold with a ruler for a rough estimate. For instance, abdominal skinfold thickness exceeding 2 centimetres in males or 2.5 centimetres in females indicates obesity. One may conduct self-assessments; by this criterion, a significant proportion of individuals exhibit abdominal obesity, even those with slender limbs.

Beyond subcutaneous tissue, a portion of fat accumulates within visceral organs, primarily within the abdominal cavity with minor concentrations around the liver. This visceral fat serves to store energy and protect internal organs. While insufficient visceral fat can harm health, excessive amounts are equally detrimental. Most people associate obesity with excessive subcutaneous fat, as this type of fat significantly impacts appearance and is readily visible. However, excessive visceral fat accumulation poses far greater health risks.