Saturated Fats are BAD FOR YOU… or are they?

We have been admonished repeatedly for decades by doctors, the American Heart Association, the press, your family and friends for eating saturated fats. But a recent study by Rajiv Chowdhury that reviewed 80 previous studies suggests that saturated fat may not change your risk of heart disease after all. The New York Times provides a nice summary of the findings…

What we know for sure:

  1. Saturated fat appears to increase both the good (HDL) and ‘bad’ (LDL) cholesterol… but the increase in LDL cholesterol appears to be limited to the large, bouyant LDL sub-type (known as LDL Type A) which is not harmful to the body, and does not increase the small, dense LDL sub-type (known as LDL Type B) which is an oxidized form of LDL and is component of the LDL that gave LDL a bad name– i.e. ‘bad cholesterol’.
  2. When we remove saturated fat from our diet (steak, french fries, burgers, cheese, whole fat milk, etc.), most people replace these calories with refined carbohydrates (bread, pasta, rice, sweets).
  3. Refined carbohydrates (which quickly convert to sugar) and added sugars are both bad for you  (see below) and should be limited to 20% total calories. Added sugar should be limited to < 10% total calories – that’s 50 grams of sugar for a 2000 calorie diet.

The problem with eating a low saturated fat diet is that fat consumption causes our brain to feel satiated (content with our meal).  So most people on a low fat diet tend to eat more calories (particularly of carbohydrates)  in their desperate attempt to feel satiated/satisfied after eating a meal. To make matters worse, our body builds a resistance (tolerance) to insulin when it’s exposed to repeated surges of the hormone that occur after eating sugary/refined carbohydrate rich meals. Imagine being yelled at repeatedly… eventually, you tune it out. Insulin resistance results in leptin resistance which makes people feel less satiated after a meal, puts the body in ‘starvation mode’ so you crave more calories and move your body less.   Insulin resistance also results in diabetes and increases your risk for heart disease, stroke, obesity, and even cancer. Robert Lustig MD summarizes this vicious cycle well:

The lead author of this recent study summarizes his thoughts nicely: “The smaller, more artery-clogging particles (LDL Type B) are increased not by saturated fat, but by sugary foods and an excess of carbohydrates,” Dr. Chowdhury said. “It’s the high carbohydrate or sugary diet that should be the focus of dietary guidelines,” he continues. “If anything is driving your low-density lipoproteins in a more adverse way, it’s carbohydrates.”

I recommend eating you should fill 1/2- 2/3rd of your lunch and dinner plate with deeply pigmented veggies (~5-7 servings=~4 cups = ~ 150 calories), and the remainder of the plate split between protein, fat, and whole grain carbohydrates.   Put another way, in a 2000 calorie diet, your calorie breakdown should be 20% carbs (400 calories, or 100 grams, divided equally between whole grains and vegetables- i.e. 50grams from whole grains, and 50 grams (~5 servings) from deeply pigmented veggies e.g. 1 serving broccoli contains 10grams carbs, 4.2grams protein, 0.6 grams fat), 40% fats (800 calories, 89 grams), and 40% protein (800 calories, 200 grams, with at minimum 1/3rd calories coming from plant-based sources).

As to whether we should be enjoying full fat milk and cheese, steaks and burgers…. I believe we need studies that examine the effects of saturated fat vs low saturated fat diet (replaced by vegetables rather than refined carbs which we know are bad for you) to clarify this important question.