What'll it be: Olive oil or bread?

We frequently discuss the advisability of consuming fats, carbohydrates, and various types within each category.

But what's the worst of all? Combining fats with carbohydrates.

Putting aside the wheat-is-worst form of carbohydrate issue and treating bread as a prototypical carbohydrate, let's play out a typical scenario, a make-believe feeding study in which a theoretical person is fed specific foods.

John is our test person, a 40-year old, 5 ft 10 inch, 210 lb, BMI 27.7 (roughly the mean for the U.S.) He starts with an average American diet of approximately 55% carbohydrates and 30% fat. Starting lipoproteins (NMR):

LDL particle number 1800 nmol/L
Small LDL 923 nmol/L

(The LDL particle number of 1800 nmol/L translates to measured LDL cholesterol of 180 mg/dl, i.e., drop last digit or divide by 10.)

Also, calculated LDL cholesterol is 167 mg/dl (yes, underestimating "true" measured LDL), HDL 42 mg/dl, triglycerides 170 mg/dl.

We feed him a diet increased in carbohydrates and reduced in fat, especially saturated fat, with more breakfast cereals, breads and other wheat products, pasta, fruit juices and fruit, and potatoes. After four weeks:

LDL particle number 2200 nmol/L
Small LDL 1378 nmol/L

Note that LDL particle number has increased by 400 nmol/L due entirely to the increase in small LDL particles triggered by carbohydrate consumption. Lipids show calculated LDL cholesterol 159 mg/dl--yes, a decrease, HDL 40 mg/dl, triglycerides 189 mg/dl. (At this point, if John's primary care doctor saw these numbers, he would congratulate John on reducing his LDL cholesterol and/or suggest a fibrate drug to reduce triglycerides.)

John takes a rest for four weeks during which his lipoproteins revert back to their starting values. We then repeat the process, this time replacing most carbohydrate calories with fats, weighed heavily in favor of saturated fats like fatty red meats, butter and other full-fat dairy products. After four weeks:

LDL particle number 2400 nmol/L