Abstract: The years are a pig killing knife, even if it is a young man who looks like Pan An and is a gentleman, people will inevitably show signs of happiness in middle age, from "mermaid line" to "big belly poop", from "small fresh meat" to "greasy uncle", and even the beautiful "white moonlight" filter will be crushed by the greasy law of middle age. Why is this happening? Let's follow the author to find out.
Men are more likely to accumulate visceral fat in the abdomen than premenopausal women. The accumulation of visceral fat in men's abdomen is a key factor in accelerating death, mainly due to the absorption of more dietary fat by their abdominal visceral fat. Because dietary fats are absorbed by intestinal cells and delivered to the circulatory system in the form of chylomicrons and very low-density lipoproteins (VLDLs), the absorption of these lipoproteins creates a huge difference between male and female body types. Chylomicrons are usually larger and more abundant in men than in women. In the postprandial state, these chylomicrons can clog the lamina propria and low-pressure lymphatic vessels.
Published in Frontiers titled "Why Do Men Accumulate Abdominal Visceral Fat?" A study (Figure 1) proposes that chylomicrons clog the intrinsic layer and low-pressure lymphatic vessels, which makes chylomicron triglycerides susceptible to hydrolysis by lipoprotein lipase (LPL), and the released fatty acids are stored by nearby abdominal visceral fat cells, resulting in the accumulation of visceral fat in the abdomen. The production of chylomicrons in men is increasing and they are more likely to accumulate visceral fat in the abdomen than premenopausal women. This accumulation eventually leads to an enlarged abdomen, giving men an apple-shaped figure.
Figure 1 Research results (Source: [1])
Natural disadvantages in physiology:
The male intestine accelerates the accumulation of visceral fat in the abdomen
How does visceral fat accumulate in the abdomen? Abdominal visceral fat (Figure 2) stores dietary triglycerides, which are digested and absorbed by intestinal cells arranged in the intestinal lumen. Intestinal cells secrete dietary triglycerides into the lamina propria in the form of very low-density lipoproteins and chylomicrons. Chylomicrons produced by men tend to enter the lymphatic lumen compared to women and are therefore more likely to remain in the lamina. The high retention of chylomicrons in the lamina propria makes their triglycerides susceptible to LPL hydrolysis, and chylomicrons deliver LPL hydrolysates to abdominal visceral fat cells posterior to the peritoneum and within the mesenteric membrane. The intraperitoneal fat banks shown in Figure 2 are mesenteric fat, small omentum fat, large omentum fat and mesenteric fat, which release fatty acids that are supplied to visceral fat cells in the abdomen before subcutaneous fat cells.
Fig. 2 Anatomy of the mesenteric and retroperitoneal membranes (Source: [1])
The accumulation of fat is the result of higher caloric intake than energy expenditure. From the perspective of fat cells, fat accumulation absorbs more nutrients than fat cells break down fat. The adipose catabolism of fat cells, also known as lipolysis, is mediated in part by epinephrine. When epinephrine binds to β adrenergic receptors, it stimulates lipolysis. Conversely, the binding of epinephrine to alpha2A adrenergic receptors leads to inhibition of lipolysis. Essentially, β receptors are lipolytic, while α2A receptors are anti-lipolytic.
Another study, titled "Estradioleffects on subcutaneous adipose tissue lipolysis in premenopausal women areadipose tissue depot specific and treatment dependent" (Figure 3), showed that estrogen reduces lipolysis in subcutaneous fat cells in the buttocks. The decrease in lipolysis in subcutaneous fat cells in women's buttocks may be due to an increase in estrogen receptor α-mediated alpha2A receptors. Estrogen stimulates an increase in these anti-lipolytic receptors in subcutaneous fat cells rather than in visceral fat cells in the abdomen, which may contribute to the breakdown of lipolysis in visceral fat cells in the abdomen of women.
Figure 3 Research results (Source: [2])
The mechanism of gender differences in abdominal visceral fat development also explains why men are more likely to produce visceral fat in the abdomen than premenopausal women (Figure 4), and due to higher dietary triglyceride intake and potential hormonal regulation, men produce larger and more chylomicrons, which trigger congestion in the lamina propria and lymphatic vessels, subjecting triglycerides to LPL hydrolysis, followed by uptake of hydrolysates by peripheral fat cells leading to the accumulation of visceral fat in the abdomen.
Figure 4 Mechanisms of gender disparities (Source: [2])
In fact, studies comparing lipolysis and nutrient absorption in various fat banks found that women had more lipolysis in the lower body fat bank than men, while men had more lipolysis in the abdominal visceral fat bank than women. Fat uptake contributes more to sex differences in fat distribution than to lipolysis. In other words, women accumulate more fat in the subcutaneous fat bank, mainly because the subcutaneous fat bank absorbs more fat than men. Similarly, men accumulate more fat in the gut bank of the abdomen because their fat bank absorbs more fat than women.
"Fat Fat Greasy" has endless troubles:
Visceral fat in the abdomen can cause metabolic abnormalities
Increased subcutaneous fat in the abdomen and intrahepatocytes is associated with a higher risk of mortality in men, but only visceral fat in the abdomen is an independent predictor of extremely high mortality in men. However, the association between abdominal visceral fat and mortality is not unique to men and is also an important predictor of mortality in obese women. Therefore, it is important to understand the relationship between visceral fat in the abdomen and metabolic complications. Studies of "High fat diet induces centralobesity, insulin resistance and microvascular dysfunction in hamsters" (Figure 5) have confirmed that a high-fat diet can lead to centripetal obesity, insulin resistance, and microvascular dysfunction in hamsters.
Figure 5 Research results (Source: [3])
Obesity affects the function of the microvascular system. Studies of male hamsters have shown that abdominal visceral obesity is not only associated with insulin resistance, but also with a decrease in capillary density and an increase in macromolecular permeability. This microvascular dysfunction, which can eventually lead to the development of hypertension, is one of the criteria for metabolic syndrome. Interestingly, the male hamsters who underwent a high-fat diet in these studies accumulated fat almost exclusively in the visceral areas of the abdomen, while the subcutaneous areas accumulated the least. This important observation suggests that a high intake of dietary fat in men promotes fat accumulation, which is quite specific to abdominal visceral reserves. Based on the above discussion, it is concluded that visceral fat in the abdomen has a large influence on the pathogenesis of metabolic syndrome.
How to break the "middle-aged greasy" law
Avoid visceral fat buildup in the abdomen?
Of all the factors that contribute to the accumulation of visceral fat in the abdomen, choosing the right lifestyle is one of the most important. According to the mechanism mentioned above, spreading dietary fat intake to eat less and more meals can effectively reduce the likelihood of visceral fat accumulation in the abdomen by reducing the size and number of chylomicrons. Reducing the lipid load of the small intestine also favors the contractile function of the lymphatic vessels, because high lipid load reduces their contraction frequency and amplitude. By maintaining lymphocystriction, eating less can reduce the dwell time of chylomicrons in the lamina. In studies of overweight youth, nibblers with higher calorie intake actually accumulated less visceral fat in the abdomen than nibblers with lower calorie consumption. The studies also took into account gender factors, namely that men are more likely than women to swallow and accumulate visceral fat in the abdomen.
Another important aspect of lifestyle is exercise. In addition to increasing energy expenditure, exercise can also slow the accumulation of visceral fat in the abdomen by increasing the flow of chylomicrons in the lamina and lymphatic vessels and by reducing the leakage of LPL and lymphatic vessels in mesenteric fat.
There are other potential factors that can lead to the development of visceral fat in the abdomen. But given that it is the independent predictor of the highest mortality rate, it is crucial to understand the mechanisms by which it develops. In short: shut your mouth and open your legs! Eat less and eat more meals, and ensure a certain amount of exercise to break the "middle-aged greasy" law!
Written by | Qiao Weijun
Typography | Luna
End
Resources:
[1] Nauli AM, Matin S. Why Do Men Accumulate Abdominal Visceral Fat? Front Physiol. 2019 Dec 5;10:1486. doi: 10.3389/fphys.2019.01486. PMID: 31866877; PMCID: PMC6906176.
[2] Gavin KM, Cooper EE, Raymer DK, et al. Estradiol effects on subcutaneous adipose tissue lipolysis in premenopausal women are adipose tissue depot specific and treatment dependent. Am J Physiol Endocrinol Metab. 2013 Jun 1;304(11):E1167-74. doi: 10.1152/ajpendo.00023.2013. Epub 2013 Mar 26. PMID: 23531620.
[3] Costa RR, Villela NR, Souza Md, et al. High fat diet induces central obesity, insulin resistance and microvascular dysfunction in hamsters. Microvasc Res. 2011 Nov;82(3):416-22. doi: 10.1016/j.mvr.2011.08.007. Epub 2011 Aug 25. PMID: 21889944.
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