Chronically low levels of blood fats indicate the presence of hypolipidemia; this relatively rare condition is usually genetic in origin, but can be a secondary condition to a variety of other ailments. Persons with hypolipidemia should be checked for thyroid function, as an overly active thyroid can cause this condition, and also for inflammation and absorptive disorders of the intestines, such as Crohn's disease and Celiac disease, which can prevent the body from absorbing fats from the diet.
For ways to naturally increase one's blood lipids, eating plenty of simple carbohydrates (i.e., sweets) and adding a moderate amount of alcohol to the diet may help. There is some speculation that adding plenty of B vitamins to the diet may also help. Eating liver and eggs is recommended.
Avoiding the things that are usually recommended as lipid-lowering strategies is also worth considering, so one should avoid garlic, limit soluble fiber, and not take in excess amounts of niacin. Fatty fish should also be avoided.