Ah, that is the question. Unfortunately, there is no nice-and-easy answer. I wish I could with confidence say “Get X percent of your calories from fat, and all will be right with the world, your health, and your pants size.”
Of course, that level of certainty would suck for people who simply don’t feel good eating X percent of fat. Aye, there’s the rub. We are all human beings, but we are not all identical in what proportion of fat/protein/carbohydrate makes us look and feel our best.
Accordingly, you may have noticed that health and nutrition experts don’t all agree on how much dietary fat is optimal. What there is a hearty level of agreement on is that whether you eat low fat, moderate fat or higher fat, the quality of your calories count. Sometimes it’s not so much about what you’re not eating (fat, carbs, etc.), but what you’re eating instead of that food category you’re avoiding.
The consensus seems to be that replacing fat, even saturated fat, with refined carbohydrates is likely to raise the risk of heart disease. Walter Willett, MD, DrPH, Chair of the Nutrition Department at Harvard School of Public Health has said that there is no benefit to reducing dietary saturated fat if those calories are replaced with “fast carbs” like white bread, sugary drinks and refined snacks.
Dariush Mozaffarian, MD, DrPH, MPH, a cardiologist and Assistant Professor of Medicine and Epidemiology at Harvard Medical School, has said that the focus on reducing saturated fat in the diet is distracting and results in illogical dietary decisions. He says that the main problem with saturated fats is that they are being replaced by low-quality refined carbohydrates, and that “what actually is important is to improve health in the diet” by:
  • Increasing consumption of fruits, vegetables, nuts, fish, vegetable oils and whole grains.
  • Reducing consumption of trans fats, salt and processed meats.

Alice H. Lichtenstein, DSc, Director of the Cardiovascular Nutrition Lab at Tufts and part of the US Dietary Guidelines Committee, advocates for moderate (not low) total fat in the diet, while limiting saturated fat.

That’s just a few examples of expert opinion. I think the takeaway here is that if you choose to eat a low fat diet, make sure that what you are eating instead of fat is high-quality, nutritious food (a la Dr. Mozaffarian’s suggestions). If you choose to eat higher total fat, make sure the fat you eat is higher in quality and includes a good proportion of monounsatured fats and omega-3 fatty acids from fish. A diet high in fat-free cookies will not serve you well, nor will a diet where you eat bacon or pepperoni with every meal.
I’ve said it before and I’ll say it again: If you eat abundant vegetables and moderate amounts of fruit while keeping hyper-processed foods to a minimum and watching your portion sizes, you have a lot of leeway in how you round out your daily calories. 
I encourage everyone, no matter what types of food you choose to eat, to go for the best quality you can, and to try to include a variety of healthy foods so that you have a better chance of getting all of the vital nutrients you need from your food. Some people do great with a lot of whole grains and legumes, others feel best with more protein and healthy fat.
Tomorrow: What goes great with a high-quality oil? A high-quality vinegar!