The McDougall starch diet – a nutritional analysis
The McDougall starch diet – how does it stack up nutritionally?
I’m always been fascinated by the sheer range of diets people eat, and frequently wonder about the nutritional content of each diet. What is the macronutrient breakdown? Does the diet give enough protein for building and repair of lean mass? Does it give you the full spectrum of essential amino acids? What about the essential fatty acids like omega 3 and omega 6 and their ratio? Does the diet miss any important micronutrients; vitamins and minerals?
I’ve been intrigued by the diet that Dr John McDougall promotes, one primarily of starches, with no added oils or fats, and no animal protein. Dr McDougall has been following and promoting this diet for 40 years.
The reason he states we should be eating a starch based diet is:
“When looked at from the perspective of human evolution, the current diet we are eating is a bizarre anomaly unlike anything we ate over the last four million years. Our blood, arteries, and cells are not designed to function under so much fat and cholesterol. Our intestines are not designed to function in the absence of fiber. Our immune system is not designed to function without an abundant supply of plant-based nutrients and phytochemicals.
With our cells drowning in fat, cholesterol, animal proteins and artificial chemicals, and our immune system is deprived of what it needs to maintain itself, it’s no wonder so many of us get cancer, heart disease, high blood pressure, adult-onset diabetes, arthritis, osteoporosis, and other age-related illnesses.”
Dr McDougall provides rationales for his recommendations on his website. You can read more here and here if you are interested.
From a nutrition science perspective, some of what Dr McDougall says is not quite correct, and I’ll write a more thorough analysis in a following post.
However the purpose of this post is to take a day of food and analyze it with respect to it’s nutritional content.
I took day 2 of the meal plan, and entered all the recipes (adjusted to a one person serve) into cronometer.com. Here is a screenshot of one part of lunch:
Many of the recipes include protein containing carbohydrates like legumes and lentils.
For the analysis I based the nutrient goals for a person who needs around 2000kcal a day, and weighs 70kg. The protein requirement for a person of this size is not less than 0.8g per kg per day. This gives a required net protein minimum of 56g per day.
You can see from the nutrient analysis the diet actually provides:
- Calories: 1688 kcal
- Protein: 61.7g
- Fat: 16.8g
- Carbohydrates: 282g
First – the number of calories would be insuffient to maintain this persons weight. Protein is only just over the minimum required as suggested by the RDA. Carbohdyrates – despite having a high percentage is 283 g per day, not particularly high. Nutrients- many exceed daily requirements, especially fibre, vitamin C and folate, which are rich in plant foods. However there are clear nutrient deficiencies.
Vitamin A retinol – While beta-carotene is high – this is the precursor to the active form of vitamin A retinol, not everyone is able to transform this. It depends on genes. Around half the Caucasian population do not convert betacarotene well to Retinol, either 30% or 60% less conversion depending on your genes. https://www.geneticlifehacks.com/beta-carotene-conversion-to-vitamin-a/
Vitamin A deficiency symptoms include: Poor night vision; dry eyes; hyperkeratosis around hair follicles, or appearing as bumps on the skin that can be mistaken for goosebumps or acne, or on the surface of the conjunctiva (Bitot’s spots); poor immunity to infectious diseases. (Chris Masterjohn)
Vitamin B12, none at all is present in a vegan diet, however Dr McDougall does recommend supplementing. In my view not enough care is taken to ensure people get adequate B12 by Dr McDougall who states:
I believe it is negligent for Dr McDougall to underplay the importance of B12 supplementation until after 3 years, you need to know where your levels are prior to starting a diet without any B12 in it. Without supplementation signs of B12 deficiency are found in over 90% of vegans. More than half of British vegans were measured deficient in B12 (Study). B12 levels must be monitored regularly.
Vitamin B12 deficiency symptoms include: Elevated homocysteine levels, megaloblastic anaemia. The neurologic symptoms include numbness and tingling of the hands and, more commonly, the feet; difficulty walking; memory loss; disorientation; and dementia with or without mood changes. Gastrointestinal symptoms: Tongue soreness, appetite loss, and constipation.
Biotin (Vitamin B7) – also a zero intake, probably because the days menu did not include any biotin sources. Signs and Symptoms of Deficiency: Scaly, red dermatitis around the nose, mouth, and perineum (between the anus and genitals), hair loss (alopecia), conjunctivitis, ataxia (loss of full control over body movements), depression, lethargy, paresthesia (tingling, numbness, or a feeling of something crawling on the skin). Biotin deficiency during pregnancy may contribute to birth defects. (Chris Masterjohn)
Vegan foods high in biotin: spinach, almonds, sweet potato, mushrooms, and cauliflower.
Vitamin E was also fairly low, vitamin E rich vegan foods include nuts, seeds and avocado. As vitamin E is fat soluble and McDougall specifically says to avoid added fats and oils, some some may end up with Vitamin E deficiency.
Calcium, although Dr McDougall states plants are a rich source of calcium, in this particular day, it is inadequate:
I’d suggest care is taken to eat sufficient calcium rich foods as well as maintain optimal vitamin D levels, to ensure you get what you need to avoid osteoporosis. (Study here shows deficiency is common in vegans)
Iodine: there is no iodine on this day – a nutrient essential for brain and thyroid function. It can be found in sea vegetables, so adding kelp or seaweed would provide this. Iodine would also be present in food if it is grown in iodine rich soil.
Protein and essential amino acids
Dr McDougall’s view on protein:
What about essential amino acids? The analysis for this day shows that all the essential amino acids are above the minimum required. However 2 points to note:
McDougall’s meal plan contains quite a lot of legumes and lentils, if these were not included (i.e. they were replaced by low protein starches like grains and root vegetables) it is likely a person would be deficient.
Plant proteins are less bioavailable than animal proteins, and even though a just adequate amount of protein is eaten, it may not be well absorbed and utilised. Protein digestibility-corrected amino ac />
The protein content in this particular day is actually fairly high for many vegan plans. As a contrast the PCRM 21 day kick start programme has around 10 grams of protein in each meal, adding to a measly 30 grams a day, which is totally inadequate by World Health Organisation (WHO) recommendations. They state: The safe requirement for humans is a recommended 0.83g/kg/day. This would work out at 58 g per day for 70kg person.
However the RDA may not even be enough, in recent studies the RDA of protein has shown to be inadequate for older men to maintain muscle mass. Muscle is a critical organ and loss of muscle called sarcopenia is a risk factor for illness and premature death. The study findings state:
“Our findings show the current WHO protein requirements are insufficient to maintain strength or muscle size in adults over age 70,” says study lead scientist Dr Cameron Mitchell, a Research Fellow at the University of Auckland-based Liggins Institute.
“The current New Zealand RDA for protein is set slightly higher than the WHO at 1.07g/kg/day (for men over 70), but still might be not enough to maintain muscle mass.”
Their study showed that twice the RDA was needed to maintain muscle mass.
Photos of the vocal proponents of plant based vegan diets show men with what appears to be low muscle mass (they are also lean – I’m not knocking that).
Dr McDougall’s views on fat:Two things which Dr McDougall states stand out:
- We have to eat essential fats
- Plants have all the essential fats we need
Lets take a look at these two statements.
First Dr McDougall does not recommends any added oils, and does not say which plant foods contain these essential fats. In his recipes he has the occasional added nuts, avocado or tofu, otherwise there are no added fats.
The nutrition analysis of this day shows the fat is extremely low. The omega 3 is all supplied from short chain alpha-linolenic acid or ALA which is poorly converted to long chain essential fatty acids EPA and DHA.
Most health organizations recommend a minimum of 250-500 mg combined EPA and DHA each day for healthy adults. This McDougall diet does not supply any EPA or DHA, and with a typical conversion rate of less than 10%, you are unlikely to get sufficient from converting ALA. So his statement that plants will give you what you need is simply not true.
Starches and Carbohydrates
As you would expect carbohydrates are high – however not overly high, with net carbs at 283 grams and fibre and hefty 52 grams. Sugars are relatively low and fructose only 9 grams. A person switching from a standard American diet onto the McDougall diet would likely decrease carbohydrates with the switch to high fibre, high water content, high nutrient and low density carbs.
Carbohydrate tolerance however varies, and some people may not do well on a high carbohdyrate diet, for example those people who have low copy numbers of salivary amylase genes.
Surprisingly a very low fat, high carbohydrate diet can improve type 2 diabetes, however this is likely due to it being low in calories and causing fat loss, including visceral, liver and pancreatic fat loss needed to reverse type 2 diabetes. An example is the Hawaiian Study which I wrote about here.
Deficiencies to watch for:
- This diet is likely to be protein deficient unless large amounts of legumes, lentils or soy are consumed
- Unless supplementary protein is consumed, it is likely you will not increase muscle mass if that is your goal
- Monitor and supplement vitamin B12
- Vitamin A and Omega 3 fats EPA and DHA are likely deficiencies for some people if they don’t convert betacarotene to retinol or ALA to EPA and DHA.
- The diet is rich in nutrient dense plant food, with low human interference
- All the rubbish food is removed – refined starch, sugar, seed oils, processed food and additives (ultra-processed food)
- Many nutrients associated with plants are high, and fibre content is high
- Overall calories are low, so weight loss would be expected
Resources for Vegans:
Jack Norris is a registered dietician who can be trusted to give accurate information on eating a healthful vegan diet. I highly recommend you visit his page.
This article is also very useful – it covers vitamin A, starch tolerance, choline, and vitamin K2.