Why do we recommend a low-fat diet?

In recent years, the long standing recommendation to eat a low fat diet has been questioned. There has been a sustained attack on low fat diets that goes beyond the rational consideration of higher fat alternatives. Language such as “Low fat diets are dead”, “old nutrition” and “the nail in the coffin for low fat diets” are not terms one would expect to hear from nutrition scientists. Neither would one expect to find that research cited to discredit low fat diets did not actually have any subjects eating low fat diets – the PREDIMED Study for example had a “low fat” group who averaged a 37% fat diet. It is interesting to consider which industry groups might have the most to lose were low fat diets to become reality rather than rhetoric – the pharmaceutical industry would be in there along with the meat, egg and dairy industries. These industry groups have become big sponsors of nutrition research.

The ongoing health debate over carbs vs fats is a gross oversimplification of the types of foods that contain these nutrients and positions animal protein beyond reproach. It sometimes seems to us that the fats vs carbs debate is a proxy used to argue for increased consumption of fat-rich animal products over starchy plant-based foods – an idea that would be quickly dismissed if it were not disguised by talking about nutrients rather than foods. It is ironic to hear of people on plant-based diets embracing the calls of the meat-based Atkins-Paleo advocates to eat a more fat-rich, reduced carbohydrate diet.

We are confident to continue to recommend a low fat diet as optimal, not because we are clinging to an outdated paradigm, but because the nutrition research of recent years has not provided good evidence to overturn the cumulative research findings of the last 50 years supporting the health benefits of a low fat plant-based diet. The following are our reasons for recommending a diet based predominantly on the low fat whole plant foods. The list includes points that are well supported by evidence from population studies, clinical trials and intervention studies, as well as other factors that we consider relevant:

  • All lean healthy populations that were free of heart disease and other Western diseases have had diets based on low-fat starchy staple foods such as rice, wheat, beans, corn and potatoes.
  • While modest quantities of olive oil were used by some Mediterranean cultures, their overall diet was largely based on grains and legumes, leaving us with no observations of the long term health effects of a diet based on high-fat plant foods.
  • The randomised controlled trials and intervention programs that have had the most remarkable results in treating heart disease (Pritikin, Ornish, Esselstyn), diabetes (Barnard) and other Western diseases have all used low-fat, high-carbohydrate, plant-based diets.
  • The plant-based nutrition experts with the most knowledge and clinical experience, with few exceptions, advocate a diet based on whole grains, legumes, vegetables and fruits – i.e. the low-fat plant foods.
  • A low-fat, whole foods, plant-based diet reduces body fat without food rationing. Starchy plant foods generally have a lower calorie density than high-fat plants and the metabolic process of converting excess carbohydrate to body fat is inefficient.
  • High intakes of dietary fat, particularly saturated fat, leads to fat accumulation in the muscle cells and liver cells, resulting in insulin resistance and type 2 diabetes.
  • The health benefits of adding nuts to a Western diet (i.e. one that is extremely low in whole plant foods) may not extrapolate to added health benefits for those already consuming mostly whole plant foods. The quantity of nuts observed to reduce health risks was only a small fraction of the diet, typically 30g per day.
  • Humans are highly adapted to starch-based diets. We have multiple copies of the starch digesting enzyme, amylase, and we even secrete it in our saliva so that starch digestion begins as we chew. Our over-sized brain uses 20% or more of our resting energy and runs exclusively on carbohydrates except during periods of prolonged fasting. Our muscles can only perform at their peak when they have been adequately ‘charged’ with carbohydrates.
  • High carbohydrate plant foods provide the resistant starch and dietary fibre that nourish healthy gut microbes. While much remains to be learnt about our gut microbiome, we know that it only takes a few days of high fibre, starchy foods to build a healthy pattern of microbes. Low carb dieters forget that most dietary fibre is composed of carbohydrates.
  • ‘Good fats’ is more an endorsement of high fat foods than a meaningful definition. Foods with moderately high saturated fat content, low omega 3 fat ratios and minimal nutrients and fibre have all been called good fats. Perhaps the term just means that there are worse fats that could have been chosen. ‘Good fats’ are said to be the reason why the Mediterranean diet is not as bad as the standard Western diet, although we suspect it’s because it’s more plant-based.
  • Most high-fat plant foods (nuts, avocados, olives etc.) have an omega 6:3 fatty acid ratio greatly in excess of the suggested optimal ratio of 4:1 or less. Flaxseed, chia seed and hemp seeds are exceptionally high in omega 3’s and may be beneficial in small quantities (amounts compatible with a low fat diet). High intakes of omega 6’s provide more precursors for the production of inflammatory omega 6 mediators and inhibits the production of anti-inflammatory omega 3 mediators.
  • Many of the plant foods that are considered to be ‘good fats’ are actually moderately high in saturated fats – 15% of calories in avocados and olive oil for example. Saturated fats are damaging to the intestinal lining, raise cholesterol levels, have adverse effects on blood and endothelial cells and increase insulin resistance. To what degree other components of whole plant foods counter these effects is uncertain.
  • Women’s health can be adversely affected by high fat intakes due to increased production and recycling of oestrogens. The excess oestrogen levels cause heavy bleeding, uterine fibroids and breast disease. High omega 6 fat intake, particularly arachidonic acid from animal products, promotes inflammation and menstrual pain.
  • Consumption of high fat foods results in lipaemic blood – centrifuge this blood and the serum layer appears milky. Lipaemic blood impairs the capacity of arteries to dilate and causes red cells to clump and stick as they flow through capillaries. High intakes of high fat plant foods may have the same effect – see this video by ultra-distance runner Randy Kreill whose diet was heavy in high fat plant foods.
  • A single high-fat meal increases blood clotting through activation of Factor VII
  • The final point is that a diet based largely on high fat plant foods is unprecedented from a population perspective and has not been adequately assessed by clinical trials. It’s an ‘experimental’ diet in comparison to the ‘evidence-based’ starch-based diet.

How much fat is OK?

After explaining why we advocate a low fat diet, people often ask us what macronutrient ratio they should aim for. We prefer to turn this reasoning around the other way, such that it’s the food group recommendations that come first, and the macronutrient ratio becomes just one of many metrics, including fibre content and calorie density, that describe this dietary pattern, recognising that whole plant foods have a composition and complexity that is not adequately described by a handful of measurements or a full nutrient analysis. We recommend a diet based on whole grains, legumes, starchy and non-starchy vegetables and fruit. Nuts and seeds are optional and are limited to a small proportion of the total diet – with the type and quantity depending on individual energy balance and health status. If you follow this pattern, then your ‘macros’ will be in the vicinity of 70-80% carbohydrate, 10-15% protein and 8-15% fat.

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Page created 26th June 2016
Last updated 4th April 2020