When is fat not just fat?
When it's visceral fat. Visceral fat is the fat that infiltrates the intestinal lining, the liver, kidneys, even your heart. It's the stuff of love handles, the flabby fat that hangs over your belt, or what I call "wheat belly."
Unlike visceral fat, the fat in your thighs or bottom is metabolically quiescent. Thigh and bottom fat may prevent you from fitting into your "skinny jeans," but its mainly a passive repository for excess calories.
Visceral fat, on the other hand, is metabolically active. It produces large quantities of inflammatory signals ("cytokines"), such as various interleukins, leptin, and tumor necrosis factor, that can trigger inflammatory responses in other parts of the body. Visceral fat also oddly fails to produce the protective cytokine, adiponectin, that protects us from diabetes, cancer, and heart disease.
Visceral fat also allows free fatty acids to leave and enter fat cells, resulting in a flood of fatty acids and triglycerides (= 3 fatty acids on a glycerol "backbone") in the bloodstream. This worsens insulin responses ("insulin resistance") and contributes to fatty liver. The situation is worsened when the very powerful process of de novo lipogenesis is triggered, the liver's conversion of sugar to triglycerides.
Visceral fat is also itself inflamed. Biopsies of visceral fat show plenty of inflammatory white blood cells (macrophages) infiltrating its structure.
So what causes visceral fat? Anything that triggers abnormal increases in blood glucose, followed by insulin, will cause visceral fat to grow.
It follows logically that foods that increase blood glucose the most will thereby trigger the greatest increase in visceral fat. Eggs don't lead to visceral fat, nor do salmon, olive oil, beef, broccoli, or almonds. But wheat, cornstarch, potato starch, rice starch, tapioca starch, and sugars will all trigger glucose-insulin that leads to visceral fat accumulation.
Fructose is also an extravagant trigger of visceral fat. Fructose is found in sucrose (50% fructose), high-fructose corn syrup, agave syrup, maple syrup, and honey.
Increased visceral fat can be suggested by increased waist circumference. The inflammatory hotbed created by excess visceral fat has therefore been associated with increased likelihood of heart attack, cardiovascular mortality, diabetes, cancer, and total mortality.
So I'm not so worried that you can't squeeze your bottom into your size 8 jeans. I am worried, however, when you need to let your belt out a notch . . . or two or three.