Good Fats and Bad Fats?

In 2014 The Big Fat Surprise was published and well reviewed. Its author, investigative journalist, Nina Teicholz had revisited the research suggesting fat is bad for us and found it seriously flawed. She concluded that we should be eating more, not less fat. So what is the truth?

We need fat

Our bodies need fat from food. It's a major source of energy. It helps absorb some vitamins and minerals. It is essential for blood clotting, muscle movement, and inflammation. That was the verdict of Harvard Health Publications in 2015 and still remains true.

However, there are different types of fat, with potentially different implications for our health.

Bad Fats – Trans Fats 

The type of fat most research indicates is bad for us is Trans-fats, sometimes known as “Hydrogenated” fats. That’s because hydrogenation is the chemical process that changes liquid oils into solid fats. It is this chemical process that is believed to lead to increased health risk.

Foods that might contain trans fats 

Pastries, biscuits, doughnuts, muffins, cakes, pizza dough, packaged snack foods (crackers, microwave popcorn, crisps), fried foods (eg French fries/chips, fried chicken, chicken nuggets, breaded fish) and candy/chocolate bars. 

Consumption of trans-fats was associated with a 34% increase in deaths from all causes, a 28% increased risk of death from coronary heart disease (CHD), and a 21% increase in the risk of CHD. That’s the conclusion from a systematic review of the evidence, published in the BMJ in 2015. 

NHS Choices reports that in 2012 most UK supermarkets and the bigger fast food chains agreed to sign up to a voluntary agreement not to use artificial trans fats. However, it notes that it isn’t clear how many products still contain trans-fats and that a 2015 report in The Guardian claimed 7,200 lives a year could be saved in the UK if trans fats were banned completely – suggesting there is still room for improvement.

The Good Fats –Monounsaturated Fats and Omega-3 fatty acids  

Monounsaturated fats and polyunsaturated fats have been widely regarded as good fats. They are important for physical well being. We describe elsewhere on Age Watch evidence for the health benefits of olive oil (a monounsaturated fat) and oily fish (rich in polyunsaturated omega-3). For example olive oil is an important part of the Mediterranean Diet, which studies have suggested can reduce the risk of heart attacks, strokes and obesity and help manage type 2 Diabetes.

Monounsaturated fats


Polyunsaturated fats/Omega–6

Omega-3 fatty acids

Olives, Nuts (almonds, peanuts, hazelnuts, pecans, cashews), Avocados, Olive oil.

Soybean oil, Corn oil, Canola (Rapeseed oil), Sunflower oil, Sesame oil, Pumpkin seeds, Soymilk.

Fatty fish (like salmon, tuna, mackerel, herring, trout and sardines), flax seed, soy, and walnuts.

Olive oil’s health benefits are provided at low temperatures, incidentally. When cooked at high temperatures the effects can be harmful. That’s because olive oil, with its relatively low smoke point of 325 to 375°F (165 to 190°C), degrades more than other oils when exposed to high heat.

We also need omega-6 foods (like vegetable oils). However, too much can be bad for us, especially when fried, cooked at a high temperature or used in processed foods. So we should eat at least an equivalent amount of omega-3 rich foods (like oily fish), to compensate.  

In addition Omega-9 fatty acids are claimed to have a number of health benefits, including helping with asthma, diabetes and high blood pressure. 

However, they have been less well studied, so more research is needed. They are commonly found in vegetable and animal fats, like canola oil, sunflower oil, olive oil, sesame oil and nut oils as well as in nuts such as almonds, peanuts and walnuts.

Vegetable oils contain a mix of different types of fat. Olive oil has the highest proportion of monounsaturated, sunflower oil the highest polyunsaturated (omega- 6), and coconut oil the highest saturated fat.

Fats in the Supermarket 

Sugar is converted into fat by your body, so ‘low fat’ foods which are rich in hidden sugar aren’t the solution. Check the sugar content in these foods first. 

Saturated Fats – good or bad for us? 

A range of respected health organisations have advised that we limit saturated fat consumption, to reduce the risk of heart disease. These include the NHS in the UK, the US Food and Drug Administration and the European Food Safety Authority. 

Saturated fats are typically found in

High-fat cuts of meat (beef, lamb and pork), Chicken with the skin, whole-fat dairy products (milk, butter and cream), cheese, ice cream, palm and coconut oil and lard.

However, in 2014 The Big Fat Surprise suggested that the original studies which led to saturated fat being seen as a risk to health were significantly flawed – and didn’t explain why a range of people eating high fat diets around the world (from the Masai in Africa to the Inuit peoples in the Arctic) were healthy and not experiencing high levels of heart disease. 

More recent systematic reviews of the evidence suggest that saturated fats aren’t a particular health risk. For instance a 2015 review in the BMJ reported that trans-fats did increase both coronary heart disease and the risk of death more generally. However, they found no clear association between higher intake of saturated fats and all- cause mortality, CHD, CHD mortality, ischemic stroke, or type 2 diabetes among apparently healthy adults. 

It is also argued that the move away from eating saturated fat has led to increased consumption of carbohydrates and sugary ‘low fat’ products – potentially increasing the risk of obesity and type 2 diabetes. 

The controversy over saturated fat is likely to continue. Until the position is clearer it would seem sensible to include saturated fat in our diet rather than consuming too much carbohydrate or sugary ‘low fat’ food to try to compensate – while at the same time not overdoing meat and dairy products. 


  • Our bodies need fat to function
  • However try to avoid trans-fats. Check food labels for trans-fats
  •  /hydrogenated fats and avoid biscuits, pastries, fried food and processed snack foods.
  • Eat foods like olive oil and nuts (good sources of monounsaturated fat and omega-9 fatty acids)
  • Also eat food like oily fish and walnuts (containing omega3 fatty acids)
  • Don’t switch to more carbohydrates or sugary ‘low fat’ food, as these increase the risk of obesity and type 2 diabetes
  • It is OK to eat meat and dairy products (sources of saturated fats) – but don’t overdo it
  • Include foods like vegetable oils, pumpkin seeds and soymilk if you wish (as sources of omega-6 fatty acids) – but don’t overdo this either.

Kayhan Nouri-Aria and Michael Baber - Reviewed and updated August 2017. Next review date July 2021.

Omega-3 rich food

Heating cooking Oil

Monounsaturated fats

The Oil Guide

Trans - fats