Adapted from Kriss Kresser article Nov 2020.
What is the optimal human diet?
There is no single optimal diet for every individual. Whether you look through the lens of evolutionary biology or biochemistry the conclusion is that the natural human diet contains both animal and plant foods.
The term nutrient density refers to the concentration of micronutrients and amino acids in any given food. Although there tends to be a high intake of calories in the standard western diet, this population tends to lack vitamin A, B6, B12, C, D, folate and iron. Deficiencies of any of these essential nutrients can contribute to the development of chronic disease and shorten lifespan. Animal foods tend to be higher in B12, iron, zinc, EPA and DHA and plant foods tend to be higher in flavinoids, carotenoids, diallyl sulphides, lignans and fibre. Therefore it makes sense to eat a range of both.
Vegetarian and especially vegan diets are lower in several essential nutrients including A, B12, D, calcium, iron, zinc, iodine, choline, selenium, creatine, taurine, methionine, glycine, EPA and DHA. For instance 92 % of vegans and 77% of vegetarians were deficient in B12 compared to 11% of omnivores in a recent study.
Omnivores and vegetarians have the same lifespan as each other and both outlive people on a standard western diet.
Both vegetarian and vegan diets are safe in pregnancy but young children are at risk of short and long term effects if their diet is too restricted.
There is no association between eating foods that are high in cholesterol and the development of heart disease. Low carb diets, that tend to be high in saturated fat, are beneficial for certain cardiovascular disease markers including body weight, triglycerides, fasting glucose, blood pressure, body mass index, abdominal circumference, plasma insulin, HDL and C-reactive protein. Current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats.
Red meat has been associated with an increase in heart disease and cancer in several studies but correlation does not mean causation. Studies show that people who eat more red meat tend to have a higher BMI, are more likely to be overweight or obese, smoke cigarettes, be physically inactive, less likely to eat fresh fruit and vegetables and and less likely to have higher than a high school education. All of these variables are associated with a higher risk of heart disease and cancer, so it becomes difficult to isolate red meat as the cause. Red meat, particularly grass fed, is rich in B12, zinc, iron, CLA, EPA and DHA that are commonly deficient in the population.
There have been ten meta-analyses of low carb diets. All ten showed that low carb diets were as effective or more effective than low fat diets for weight loss. Some individuals of course may do better on a moderate carb or even high carb approach.
For type 2 diabetics, low carb diets are more effective than high carb diets for weight loss and also improve cardiovascular markers. Low carb and ketogenic diets are more effective than hypo-caloric or low fat diets for improving glycaemic control in type 2 diabetes.
Meanwhile politics, religion and poor science used in nutritional epidemiology have resulted in a lag in change from many institutions who give advice on diet such as the American Dietetics Association, American Heart Association and the American Diabetes Association.
In studies the Paleo diet has compared well against the Mediterranean and low fat diets.
Studies have found that ketogenic diets improves cardiovascular risk factors and have been shown have a beneficial effect in Parkinson’s disease, Alzheimer’s disease and dementia, and epilepsy, and also traumatic brain injury.
The carnivore diet is an “all meat diet” is gaining traction. Although this may improve chronic health problems in the short term, the long term effects are not known. Further research is required.
In general, on urine testing, animal foods are acid forming and plant foods are alkaline forming. However the blood pH is tightly controlled regardless of what you eat.
The low fat, vegan and Paleo diet advocates all don’t eat full fat dairy for various reasons. Dairy is the only food group that has more saturated than unsaturated fat. Meat, including red meat, pork and eggs all contain more unsaturated than saturated fat. Studies show that people who consume more full fat dairy products have either the same or a lower risk of obesity, diabetes and cardiovascular disease.
There is a degree of controversy over the environmental cost of meat eating. There are certainly harms from intensive meat rearing. On the other hand properly managed live stock can regenerate grassland ecosystems and reduce carbon emissions.
It is fully understandable that people who love animals and don’t want to see them mistreated embrace veganism and vegetarianism. Better animal husbandry and methods of transport and slaughter need to be more widespread.