Fat: The Good, the Bad and the Ugly

  • There is a role for fat in a healthy dietary pattern and moderate fat containing dietary patterns enriched with olive oil and nuts are among the best documented to show major health benefits and longer survival.
  • Know the good fats: polyunsaturated fats, monounsaturated fats and essential omega 3 and 6 fatty acids.
  • Know the bad fats: trans fat with no role in a healthy diet.

Fat: an important macronutrient

Fat is the general name for a type of macronutrient that along with carbohydrates and protein, provide energy for our body. Fats provide 9 calories per gram compared to 4 calories per gram of carbohydrates or proteins. Fat is essential to health and is important for many reasons including: absorption of many vitamins, lowered inflammation, as well as electrical stability of the heart.  For years fats have been demonized and the simple message for good health was to just eat “low fat” but this has resulted in unintended health consequences.

Fat and unintended consequences

Despite decades of institutional recommendations to reduce fat and particularly saturated fats we are not healthier as a nation. On the contrary, the low fat campaign has paralleled a disturbing trend where currently two out of every three Americans are either overweight or obese.  Along with the nutrition message to reduce or eliminate fat in the diet, food manufacturers responded with new products in which saturated fat and cholesterol were replaced with added and hidden sugars. This provides improved taste and palatability and a bonus: longer shelf-life. Lower fat foods now rich in refined carbohydrates and sugars set the stage for further weight gain as a nation and a very common condition affecting nearly 50% of Americans called insulin resistance that often shows up as prediabetes and type 2 diabetes.

In the 1960s, Americans consumed about 45 percent of calories from fats; about 13 percent of adults were obese and less than 1 percent had type 2 diabetes. Today, Americans eat less fat, making up about 33 percent of calories; nevertheless, obesity levels have nearly tripled and more than ten times more adults are diabetic.

Research on the types of fat and how nutrients are substituted within an overall diet has led to the prevailing idea that it is the overall dietary pattern (and quality) and not the percentage of fat or saturated fats that matters for health. According to leading expert on nutrition and cardiac health, Dr. Ron Krauss, Senior Scientist and Director of Atherosclerosis Research at Children’s Hospital Oakland Research Institute, Adjunct Professor in the Department of Medicine at University of California, San Francisco,

“Rather than focusing on saturated fat as a top priority for heart disease risk, one really needs to look at overall diet in which saturated fat is eaten”

Different fats different effects

Saturated fats: a saturated fat is solid at room temperature. Imagine bacon grease after it has cooled. There is little direct evidence to  support the notion that saturated fats cause disease. For decades it was believed that since saturated fat increased cholesterol levels this alone was justifiable evidence to limit saturated fats in the diet. After all more cholesterol, more heart disease. In reality, studies have failed to demonstrate the expected lowering of heart disease events such as heart attacks and strokes. Many studies that replaced dietary saturated fat with carbohydrates failed to show benefits and in fact some showed an increased number of adverse outcomes. On the other hand, replacing saturated fats with polyunsaturated fat or monounsaturated fat in the form of olive oil, and nuts did not show harm and many demonstrated significant benefits with reduced heart disease events and improved survival. The literature on this subject continues to evolve and we know that all saturated fats are not necessarily “bad”.

  • Randomized controlled studies show dark chocolate lowers many risk factors of cardiovascular disease and has a high content of stearic acid, a saturated fatty acid that does not increase cholesterol. Recent evidence finds more distinctions within saturated fats based on the molecular structure and the number of carbon atoms. Those saturated fats associated with increased dairy consumption: whole milk, cheese, yogurt contain an odd-number of carbon atoms and are associated with a lower risk of developing type 2 diabetes.

Essential fatty acids: There are two types of fatty acids that mammals are unable to synthesize. and are considered “essential fatty acids”.  These two fatty acids an omega-6 called linoleic acid (LA) and an omega-3 called alpha linolenic acid (ALA) that must be supplied by the diet.

Polyunstaturated fats (PUFAs): Most studies suggest that replacing saturated fatty acids with PUFAs lowered the risk for CHD events by about 25%. Polyunsaturated fats contain more than one double bonds.

Monounstaturated fats: These fats from plant sources contain just one double bound and examples of foods high in monounsaturated fats include plant-based liquid oils such as: olive oil, peanut oil, safflower oil and sesame oil. The interest in some high fat diets rich in olive oil and lower rates of cardiovascular diseases developed from the the controversial Seven Countries Study more than 50 years ago and more recently in the Mediterranean dietary pattern. The PREDIMED study demonstrated the benefits of a Mediterranean dietary pattern enriched with monounsaturated extra-virgin olive oil (50 cc per day) or mixed nuts (30 grams per day) and showed a 30% lowered risk of heart attack, stroke and cardiovascular death as well as improved cognition and less dementia. Almonds are rich in monounsaturated fats that make-up more than 60 percent of the total fat grams and walnuts are rich in alpha linolenic acid.  Another rich source of plant-based healthy fats are avocados.  They are 85% fat, 66% of which is monounsaturated and 12% is polyunsaturated.


Trans-fats (partially-hydrogenated fats)Polyunsaturated Fatty Acids (PUFA) are liquid at room temperature (vegetable oils).  Saturated fatty acids are solid at room temperature (animal fat).  Trans fats are created in the artificial process of converting polyunsaturated fat into a more saturated fat.  Trans fatty acids are also known as partially hydrogenated oils and are particularly dangerous not only do they raise bad cholesterol (LDL-C), and lower good cholesterol (HDL-C) but many observational studies demonstrate an increased risk for heart attack, sudden death and type 2 diabetes.

  • The Nurses’ Health Study (more than 120,000 female nurses) demonstrated the effect of trans fat on heart disease risk and found cardiovascular disease risk roughly doubled for each 2% increase in trans fat calories consumed (instead of carbohydrate calories) on 14 years of follow-up.

Trans fats may be hidden in fried foods like French fries and doughnuts, and baked goods including pastries, pie crusts, biscuits, pizza dough, cookies, crackers, and stick margarines and shortenings. Trans fats (partial hydrogenation) increase shelf life and flavor stability of foods containing fats. Good for the food industry but not so good for our health.

  • The FDA has recently (June, 2015) gave the food industry three years to eliminate artery-clogging artificial trans fats from the food supply. This represents a long-awaited step and is expected to save thousands of lives a year.

Omega-3 fatty acids are required for numerous normal body functions, including: controlling blood clotting and building cell membranes in the brain and are associated with protection against heart disease and possibly stroke. Clinical studies are ongoing in regard to benefits for such conditions including cancer, inflammatory bowel disease, and other autoimmune diseases such as lupus and rheumatoid arthritis. Omega-3 fatty acids can exert cardio-protective effects via multiple mechanisms. They can prevent cardiac electrical instability (arrhythmia), have anti-inflammatory effects and can prevent hardening of the arteries (anti-atherosclerosis properties) by their effect on certain forms of fatty acids called prostaglandins that improve blood vessel dilatation (increase endothelial-derived nitric oxide) and help prevent abnormal blood clotting (anti-thrombotic).

Two sources of omega-3s

There are two major sources of omega-3 fatty acids in our diets: one type is represented by a plant-source: alpha-linolenic acid (ALA), which is found in some vegetable oils, such as soybean, rapeseed (canola), and flaxseed, walnuts and some green vegetables, such as Brussel sprouts, kale, spinach, and salad greens. The other source is marine-based and found in high amounts in cold-water fish.

Both vegetable and marine sources of omega-3 fatty acids have health benefits. Most Americans do not get enough omega-3s in the diet so consider: a daily serving of a handful of walnuts or ground flaxseed mixed into your morning oatmeal can provide more omega-3 fats.  A tablespoon of canola or soybean oil in salad dressing or in cooking, or one serving of a fatty fish (such as salmon) can provide adequate omega-3 levels. In general higher omega-3 levels are associated with lower rates of death from any cause from sudden cardiac arrest, and with slower rates of cellular aging.

  • There is positive evidence of higher omega-3 blood levels and associated lowest risk of cardiac arrest (sudden cardiac death). Higher omega-3 fatty acids blood levels compared to lower levels in healthy individuals aged 65 and older -without preexisting heart disease were associated with nearly a 30% lower risk of cardiovascular death.
  • More fish is good for diabetes prevention: (Diabetes Care. 2014;37:189–196).  Omega-3 fats in general have had favorable associations with various measures of health including a beneficial or effect on type 2 diabetes. A new population-based cohort study found that higher blood levels of omega-3s (a marker of fish intake) is linked to a lower long-term risk for type 2 diabetes. Those participants with the highest omega-3 intake lowered diabetes rate by 33%

Fish for health and some cautions

High concentrations of mercury, a neurotoxin that can damage developing brains in fetuses, are found in some kinds of popular fish such as albacore tuna. Swordfish and shark, king mackerel, marlin, orange roughy and tilefish also contain dangerous levels of mercury.

Women of reproductive age and young children are advised to avoid these types of fish and limit overall consumption of all fish to no more than 12 ounces per week, according to the Food and Drug Administration, as it takes months for the body to rid itself of mercury. The Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) consider five of the most commonly eaten fish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Another commonly eaten fish, albacore (“white”) tuna has more mercury than canned light tuna.

It is advisable to limit albacore tuna to about one meal per week (about 6 ounces one average meal). The American Heart Association recommends eating fatty fish at least twice a week because it is high in omega-3 fatty acids. Fatty varieties that are low in mercury include wild salmon, herring and sardines.


The correlation between fat and heart disease is complicated and as the science has evolved we know fat is not as bad as once thought.  There is a role for fat in a well balanced diet with notable health benefits within a healthy dietary pattern.

Mozaffarian D, et al. Plasma Phospholipid Long-Chain omega-3 Fatty Acids and Total and Cause-Specific Mortality in Older Adults: A Cohort Study. Annals of Internal Medicine 2013;158:515-25

Chowdhury R, et al. Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis. Annals of Internal Medicine 2014;160:398-406.