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From weight management and balanced metabolism prospective fatty acids or fats are not that bad at all. Most important positive aspect of fats is that their consumption results in reasonable satiety and does not induce unreasonable food cravings. The negative side of fat consumption is that they are energy dense.  Energy density is an amount of potential energy contained per volume. Many fruits and vegetables have low energy density because they are comprised of nutrients along with energy free fibers and water. Fatty acids do not mix well with water or fibers.  As a result most fats are constrained within a very small physical volume. One table spoon of olive oil is 120 calories. It is about the same amount of energy as a big size apple would have. Now imagine how easy it is to put two instead of one tablespoons of oil in salad and how much of extra work it is to eat an extra apple.

Digestion of one gram of fat releases 9 calories of energy, more than double of the amount of energy released from proteins or carbohydrates.

In terms of energy equivalents per gram the macronutrients hierarchy look something like this:


- fats 9 calories per gram

- carbohydrates 4 calories per gram

- proteins 4 calories per gram, but some of that energy, at times as high as 25-30% may be wasted as thermal energy


In terms of energy equivalents per volume the hierarchy is slightly different:

- fats are the most dense

- proteins

- carbohydrates are likely the least energy dense


Group of Fatty acids is the most controversial group at the moment. Despite of being very energy dense, it is not directly linked as a cause for obesity, as long as calories are acknowledged. Fats are Ok to include in low carb diets. At one point fats were linked to atherosclerosis. Low fat high carb diets were introduced. Many authorities now link low fat/high carb diet to the epidemic of obesity we are fighting with right now. Todays view about relationship between fats and cholesterol is described below.


Other than high calorie density, the most important point to understand about fats is that there are bad and good fats in terms of their affect on our health. From weight management prospective there is little difference between good and bad fats. Without going in great chemical details let's concentrates on names only

- trans fats, also labeled as "partially hydrogenated" oils are mostly manmade fats (but some trans fats are also present in some animal fats) and they are the worst of any fats for our health. They are usually made by hydrogenating the vegetable fats which make their consistency more hard, increases their shelf life. Common sources in our diet are commercially baked products with eternal shelf life thanks to these fats, some commercial  deep fried food (oils kept at a high temperature is one of the common sources), processed food, cakes, cookies, some margarines. These fats need to be ideally excluded completely.

- saturated fats generally animal origin and hard. They raise cholesterol level and they should be avoided. 

- unsaturated fats is somewhat diverse group which is further classified in mono unsaturated fats (olive oil, canola oil), which are likely neutral or somewhat beneficial for our health. Polyunsaturated n-6 fatty acids (sunflower, safflower, corn oils) are likely beneficial for our health.  Mostly word unsaturated is associated  with healthier fats. Most  unsaturated fats are of vegetable or seafood origin, usually liquid consistency, most of them are considered to be healthy.  

- Omega 3 fatty acids (Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)) or other name is n-3 polyunsaturated acids might deserve a separate discussion. Just like vitamins, humans need to get Omega 3 fatty acids with food, because we are unable to produce them. Good sources are mostly fish and to some degree vegetable oils like flaxseed oils. They improve cholesterol profile, have anti-inflammatory properties and multiple other health benefits. To the best of my knowledge there are no known negative effects discovered so far from Omega -3 Fatty acids supplements.

We recommend that most adults who are seeking information on a healthy diet be counseled to consume at least one to two servings per week of oily fish. We suggest that most adults who do not consume this much fish take a daily fish oil supplement (about 1 g/day)


Official Guidelines:


The 2015 Dietary Guidelines for Americans recommend that, for adults, between 20 and 35 percent of energy should come from fat. Among 4- to 18-year-olds, the recommendation is 25 to 35 percent, and 30 to 40 percent for children one to three years of age. These guidelines also recognize the importance of type of fat, as reflected in the following advice:

Consume less than 10 percent of calories from saturated fatty acids by replacing them with monounsaturated and polyunsaturated fatty acids.


Keep trans fatty acid consumption as low as possible by limiting foods that contain synthetic sources of trans fats, such as partially hydrogenated oils, and by limiting other solid fats.


Reduce the intake of calories from solid fats. Use oils to replace solid fats where possible.


Replace protein foods that are higher in solid fats (eg, red and processed meats), with choices that are lower in solid fats and calories and/or are sources of oils. These include seafood, legumes (beans and peas), and nuts, seeds, and soy products, as well as lean meats, poultry, and eggs.

20-35% of energy should come from fats

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