Low fat diets for weight loss

The diet we recommend for weight loss is a high carbohydrate, low fat diet, with modest but adequate amounts of protein. These macronutrient proportions, rather than being targets, are secondary to having a diet based on whole grains, legumes, starchy and non-starchy vegetables and fruits. The typical fat content of meals based on these food groups is around 10% of calories, far below the 30% fat diet that many researchers call a ‘low fat diet’. Typical fibre contents for this diet are in the order of 60g per day which is also far different to the diets typically used in high carb vs high fat diet research (usually 15-20g fibre).

While there is a lot of controversy about the healthy range of fat intakes for humans, the fact remains that a low fat diet, based mainly on starchy plants, keeps people lean. Dr McDougall often makes the point that all large populations of lean healthy people have eaten starch-based diets – rice in Asia, sweet potatoes in PNG, taro in the Pacific, corn and beans in North America, potatoes in South America and in the past, wheat and barley in Europe. If this is not enough to dispel the notion that carbs make you fat then consider some of the best known and well researched plant-based diet programs – Pritikin, McDougall, Ornish, Barnard and Esselstyn – all high carb, low fat diets, and all get spectacular weight loss results, and good long term adherence.

Now for some theory. Protein and carbohydrate both have 4 calories per gram while fat has more than twice the calories, with 9 calories per gram. It’s already not looking good for low carb diets (which are always high in fat), but it gets worse. The fat we eat is readily stored as body fat with an efficiency of 95% (only 5% of calories lost in the process). In contrast, carbohydrates in excess of our immediate needs are not readily stored as fat. They are used as fuel for our metabolic processes and stored in liver and muscles as glycogen – the storage form of glucose, the preferred fuel for our brain and muscles. The conversion of carbohydrates to fat (de novo lipogenesis) does not occur readily in humans and when it does, the efficiency is only 75% (that means that 25 out of 100 calories of excess carbohydrate are lost when those carbs are trying to make you fat).

The gut microbiome and its interaction with gut hormones is an emerging area of research and may influence the development of obesity. A plant-based high carb diet is a winner in this respect too. It provides the resistant starch and other classes of dietary fibre that best support a healthy profile of gut microbes (See: Resistant starch).

While there are experts who argue that eating less carbs and more high fat plant foods – nuts, seeds, avocados, soy, and even olive oil – may be healthy, the evidence is very much in favour of a low fat, whole foods, plant-based diet.


Peer-reviewed articles:

Research purporting to show low fat diets “don’t work”

Several recent studies including systematic reviews and meta-analyses have claimed that a low-fat diet is no better, or is less effective than low-carbohydrate diets for weight loss and also for various chronic diseases. The key point to understand with these studies is that they did not use a low fat diet as defined by plant-based experts (10-15% calories), rather they have used diets which averaged between 29%-37% fat and have claimed them as “low-fat”.

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Page created 14 February 2016

Page last updated 8 September 2016