Carbohydrates are the primary source of body fat for most, not fat. Which is probably why the ketogenic diets work so well.
Insulin is the main fat-building hormone. After consuming a plate of pasta (or other high carb meal), your blood sugar will rise and your insulin level will rise as well (unless you are a type 1 diabetic and do make insulin), to prevent a jump in blood sugar. All the blood sugar that is not used as energy or stored (as glycogen) is turned into fat.
Fatty acid building blocks of fats can be metabolized (burned), stored, or converted by your body into other compounds (depending upon what is required). Fat is always in flux in the body, being stored, put into the blood, and being converted to energy. The amount of triglycerides (storage form of fat) in your bloodstream at any time is determined by your heredity, your level of exercise, your blood sugar levels, your diet, your ratio of abdominal fat to lean body mass (muscle), and especially by your recent consumption of carbohydrates! Dietary fat can’t be converted into blood sugar, therefore fat doesn’t cause serum insulin levels to rise.
Slim and fit people tend to be very “sensitive” or “responsive” to insulin and have low serum levels of triglycerides and insulin. Even the slim and trim will have higher triglyceride levels from excess blood sugar after a high-carbohydrate meal (this is why lipid and glucose blood panels often require 12 hours of fasting). The higher the ratio of abdominal fat to lean body mass, the less sensitive to insulin you will be, and the more insulin your body needs to produce. In the obese, triglycerides are ususally present at high levels in the blood stream all the time. High triglyceride levels are a direct cause of insulin resistance and they contribute to fatty deposits on arterial walls (atherosclerosis, as well as cardiovascular diseases).
If you become (or are) overweight, you will enter the vicious cycle: you will produce more insulin, become insulin-resistant (which requires you to make even more insulin), and become more overweight because the body will create and store more fat. This can be reversed by eating less carbohydrate, normalizing blood sugars, and slimming down.
In theory . . . you could acquire more body fat from eating a high-carb fat-free dessert than you would from eating a tender steak (marbled with fat). However the fat in the steak is more likely to be stored if it is accompanied with bread, potatoes, corn, or other high carbohydrate foods.
You control your health. Talk to your naturopathic doctor or nutritionally minded health practitioner today about a healthy diet full of vegetables, quality proteins, and essential fats; as well as screening lab tests (fasting glucose, triglycerides, insulin, etc.), an exercise program, and weight loss. If you believe you need help with label reading, food recommendation, healthful recipes, and shopping advice there are professionals to help.