The American Medical Association started aggressively campaigning in the 1970's that a healthy diet is one that is consistently low in fats. and they have maintained that message as the "party line" ever since. Today, you can't go to the grocery store without seeing row upon row of foods advertising themselves to be "low fat", "nonfat" or "fat free," constantly bombarding you with the subliminal message that fats are bad for you. Meanwhile, forty years later, America is facing an epidemic of obesity that is contributing to a host of health problems, not only for aging adults but also for young children.
Is there, then, a relationship between low-fat diet and obesity? Gary Taubes, for one, thinks so. In his book, Good Calories Bad Calories , he presented an overwhelming amount of evidence to show that the easiest and most effective way to lose weight is to adopt a high-fat, low-carb diet. A high-protein diet can not be sustained, because after a while the dieter just can't face another lean pork chop. With a high-carb diet, the dieter is constantly suffering from hunger pangs, while losing little if any weight. But a high-fat diet, such as the Atkins diet, works relatively painlessly, in part because fats take longer to digest, and leave you feeling more satiated.
It might seem logical, since fatty tissue is made of fat, that a low-fat diet might help prevent you from becoming fat. Ironically, exactly the opposite is true. Humans are fully capable of manufacturing fats from carbs -- a process that takes place in the liver with the help of insulin. These manufactured fats are then dispatched to distributed locations throughout the body, where they can be stored away in fat cells for later use. My belief is that, once biological monitoring mechanisms recognize that there is a distinct shortage of fats in the diet, the appetite is automatically adjusted upwards, to compel the person to consume more calories in a given day than they can burn off. This has the intentional effect of accumulating a store of reserve fats on the body, a metaphorical silo, which can then provide a steady stream of fat nutrients to the muscles and brain to overcome the glaring deficiency in the diet.
If, in addition to consuming a low fat diet, the person also aggressively avoids the sun, then the problem will be compounded, and they will likely gain even more weight. This is because of the role calcium plays in the efficiency of fat metabolism, and the role vitamin D plays in the absorption of calcium.
It has now become evident that not all fats are created equal. The culprit that's responsible for the "fats are bad" message is partially hydrogenated oil, or "trans fats." These synthetic fats are created by loading up liquid vegetable oil with hydrogen and then heating it, along with a metal catalyst, to a high temperature. The result is a fat that stays solid at room temperature and survives a long time on the shelf. Once companies figured out how to do this well, all kinds of processed foods, most notably margarine, but also crackers and cookies, started appearing on the grocery shelves. These products don't get rancid at room temperature because even the microorganisms that would spoil them are smart enough not to consume them. If you consume them in large quantities, your "LDL" (bad) cholesterol levels will go up, and your "HDL" (good) cholesterol levels will go down  (Wikipedia) . A survey issued by the Food and Drug Administration in 1999  (Trans Fats Survey) determined that these fats constituted 95% of the cookies, and 100% of the crackers found on supermarket shelves. Companies are now scrambling to find ways to replace the trans fats in all their products.
The media recently has begun to sing the praises of "Omega 3" fats, found in large amounts in fatty fish such as sardines and salmon. Researchers have discovered that eskimos, whose diet is extraordinarily high in fat, have excellent health with respect to heart disease prognosis. A recent study by Fombonne et al. found that the Inuits of northern Quebec appear to be completely free of autism . Not a single case was found among their children. This fits well with the theory presented here, since they eat an extremely high fat diet, consisting of large amounts of seal blubber and fatty fish like salmon. These are both excellent sources of both fats and vitamin D.
Unfortunately, pregnant women have in recent years been discouraged from eating fish, due to the high contamination with mercury, which is believed to cause damage to the developing fetus. It is frustrating that mercury contamination (a valid concern) stands in the way of getting adequate omega 3 fats for the baby. However, recent studies have pretty much dispelled the theory that mercury might cause autism. Several studies have now confirmed no link between mercury and autism. In fact, in California, after mercury was eliminated from the vaccines, the incidence of autism continued to rise  (Mercury and Autism) .
Although fish is the best source, a surprising number of pallatable foods also contain Omega 3 fats, including walnuts, strawberries, tofu, cauliflower, spinach, and scallops  (Food Sources of Omega 3 Fats) .
As has been convincingly shown by the Nurses' Study, if you want to become pregnant, you will significantly improve your chances by enjoying plenty of whole milk, butter, and ice cream. You will also, in my view, significantly improve the chances of producing a healthy child by continuing to maintain a high fat diet throughout the pregnancy, and while you are nursing the baby. It is important, however, to choose foods carefully so as to assure a good steady supply of omega 3 fats, and to religiously avoid consuming trans fats. There is no place for a low fat diet during pregnancy and lactation.
1. Gary Taubes, Good Calories Bad Calories:Challenging the Conventional Wisdom on Diet, Weight Control, and Disease., Alfred A. Knopf., 2007.
4. E Fombonne, J Morel, J Macarthur, "No Autism Amongst Inuits From Northern Quebec," Fifth International Meeting for Autism Research, 2006
5. Dr. R. Schechter, "Continuing Increases in Autism Reported to California's Developmental Services System," Archives of General Psychiatry. 2008;65(1):19-24, January, 2008.