If I were granted the magical power to expunge just one word from the popular discourse, it would be “carbs”. “Protein” would be a close second, at least in the context of “eating protein”. Heck, if the genie threw in a third wish, I’d seriously consider calling for instantaneous delivery of electric shocks to any health professional or internet talking head who yaps about “eating carbohydrates” or “eating protein”, regardless of whether they’re advising their hapless “followers” to eat more of them, or less of them. People don’t eat “carbohydrates”, and they don’t eat “protein”. People eat food… or at least, something masquerading as food.

If they’re eating actual food (that is, whole or minimally processed food, such as an apple, a potato, chick peas, an egg, a pork chop, or home-made sourdough bread), they’re consuming complex mixtures of macronutrients and micronutrients, embedded in a matrix of what has been described as “nutritional dark matter“. Nutritional dark matter comprises a plethora of as-yet-undiscovered, or discovered but as-yet-uninvestigated molecules that exert as-yet-unknown or barely-known effects on human health. It’s highly likely that many of the apparently contradictory results of nutrition research studies are attributable to the interaction between nutritional dark matter and the infinite genetic, epigenetic and environmental variations that make each human being unique.

And if people are eating “edible food-like substances”, to borrow Michael Pollan’s memorable phrase, they’re consuming complex mixtures of macronutrients, micronutrients (both naturally-occurring and laboratory-synthesised), and a host of food additives whose effects on human health are vastly under-investigated.

Consequently, anyone who tells you that the key to improving your health is either to eat a “low carb” or “high carb” or “low protein” or “high protein” diet, is, to put it kindly, underinformed. Instead, it’s the nutritional matrix in which that protein or carbohydrate is embedded, that determines its effect on health. “How much?” is the wrong question to ask. “Where does it come from, and what does it travel with?” is the right question.

Carbs ain’t carbs¹

The Nurses Health Study is one of the largest and longest-running investigations of factors that influence women’s health. When researchers investigated the association between 47 513 participants’ dietary habits (assessed with serial food frequency questionnaires) and their likelihood of aging healthfully (“defined as surviving [at least] to the age of 70 years while being free from 11 major chronic diseases², having no impairment in memory or physical function, and being in good mental health”) over a 30 year follow-up period, they found that high–quality carbohydrate intake increased the likelihood of healthy aging, in a dose-dependent manner, while refined carbohydrate intake had the opposite effect.

Specifically,

• For each additional 10 per cent of overall calorie intake derived from carbohydrate, participants’ odds of healthy aging rose by 17 per cent.
• For each 10 per cent increment in intake of high-quality carbohydrates derived from whole grains, fruits, vegetables, and legumes, odds of healthy aging increased by 31 per cent.
• Every 10 per cent increment in intake of refined carbohydrates derived from foods such as white bread, bakery items, sugar-sweetened beverages, sugary cereals and other ultraprocessed foods, decreased the odds of healthy aging by 13 per cent.
• Overall fibre intake, and fibre derived from fruits, vegetables, and cereals, were all associated with higher odds of healthy aging.
• Higher glycaemic index diets, and diets with a higher carbohydrate-to-fibre ratio (that is, more carbohydrate and less fibre) decreased the odds of healthy aging.

The researchers also conducted substitution analyses, modelling the impact of swapping 5 per cent of daily calories from either total carbohydrate or high-quality carbohydrate for various other macronutrients. The figure below illustrates the effects of these substitutions. If the square is on the left of the vertical line, the substitution favours healthy aging and vice versa. If the horizontal line crosses the vertical, the result is not statistically significant (i.e. could have been due to chance rather than a genuine association).

The distinctions between the impact of total carbohydrate and high-quality carbohydrate are intriguing. So if participants dropped their intake of animal protein from foods such as meat or eggs by 5 per cent, and replaced the ‘lost’ calories with the exact same number of calories derived from any old carbohydrate, they would decrease their odds of healthy aging by 7 per cent. Swapping plant protein from foods such as legumes, whole grains and seeds out for an equal-calorie amount of total carbohydrate, was an even worse deal, decreasing the odds of healthy aging by 37 per cent.

But if animal protein was replaced with high-quality carbohydrates from legumes, whole grains, vegetables and fruits, the odds of healthy aging were boosted by 8 per cent, while the plant protein-to-high-quality-carbohydrate swap lost statistical significance – probably because it entailed swapping one healthy plant food for another healthy plant food!

Notice that swapping fat out for an equivalent-calorie amount of either total carbohydrate, or high-quality carbohydrate, was beneficial for healthy aging.

One final note: sadly, a mere 7.8 per cent of the 47 513 participants, who had reached ages between 70 and 93, met the full definition of healthy aging. 31.7 per cent were free from all 11 chronic diseases considered in the study, 48.8 per cent did not report impairments in memory, only 15.3 per cent had no physical function limitations, and 38.3 per cent maintained good mental health. Bearing in mind that all participants had been nurses at the time of enrolment into the study, this pathetically low rate of healthy aging speaks volumes about the glaring deficits in the “health care” system. Women who had spent their working lives in that system apparently knew so little about actual health, that less than 10 per cent of them reached old age in good physical, cognitive and mental condition.

Protein ain’t protein

Nurses Health Study data have also been mined to investigate the effects of protein on healthy aging and, once again, the source of the protein turns out to be even more important than the quantity of protein ingested.

For example, using the same criteria for defining healthy aging as in the total vs high-quality carbohydrate study discussed above, a higher intake of total protein in midlife was associated with better odds of healthy aging, but plant-derived proteins were significantly more potent. After adjusting for multiple potential confounding factors, for every additional 3 per cent increment of total calories that participants obtained from protein:

• Total protein (i.e. protein derived from any source) increased the odds of healthy aging by 5 per cent
• Animal protein increased odds by 7 per cent
• Dairy protein increased odds by 14 per cent
• Plant protein increased odds of healthy aging by 38 per cent.

In substitution analyses, only plant-derived protein delivered favourable effects on healthy aging when swapped in for other macronutrients or sources of protein:

Likewise, in both middle-aged men and women, higher plant protein intake is associated with decreased risk of cardiovascular disease and coronary artery disease and lower all-cause mortality and cardiovascular mortality, while higher animal protein intake is associated with increased cardiovascular morbidity and mortality.

Plant protein is also protective against development of frailty in older women, while a higher animal protein intake increases risk of frailty. And substitution of 5 per cent of calories from plant protein intake at the expense of animal protein was associated with 38 per cent reduced risk of frailty, while replacing 5 per cent of energy from dairy protein with plant protein reduced frailty risk by 32 per cent, and from non-dairy animal protein by 42 per cent.

Plant-based ain’t plant-based

As many vegans and vegetarians end up discovering, a plant-based diet is not necessarily a health-promoting diet. While a wholefood plant-based diet comprises all the foods that have been repeatedly shown to reduce morbidity and mortality – fruits, vegetables, whole grains, legumes, nuts, seeds, herbs and spices – there are also plant-based junk foods comprised of ingredients definitively linked to ill-health and premature mortality – refined carbohydrates, sugar, junk fats and oils, and food additives.

When researchers analysed data from the European Prospective Investigation into Cancer (EPIC) and UK Biobank cohorts, in participants aged 35–70 years at recruitment, they found that healthy plant-based diets were associated with reduced multimorbidity (i.e. having more than one illness at the same time) of cancer and cardiometabolic diseases, while unhealthy plant-based diets may increase the risk of multimorbidity. The figure below shows the effect of high intake of healthy plant-based foods (A) and unhealthy plant-based foods (B) on the risk of developing cancer, cardiovascular and diabetes, and the risk of progressing from one of these conditions to multiple. Remember that a square (for the EPIC cohort) or a circle (for the UK Biobank cohort) to the left of the vertical line means that the diet reduced the risk of illness and vice versa; horizontal lines that pass through the vertical indicate that the association was not statistically significant.

It’s important to point out that neither this study, nor those cited in the previous section on animal vs plant-derived proteins, demonstrate that 100 per cent plant-based diets are necessarily more healthful than diets than contain mostly plant-derived foods. A diet rich in fruits, vegetables, whole grains, legumes, nuts and seeds, with a small amount of free range eggs, wild caught seafood and fermented dairy products, is very obviously more health-promoting than a vegan diet comprised of sugary breakfast cereals, white bread, two minute noodles, hot chips and Oreos (and yes, I’ve seen more than a handful of vegan clients who are attempting to live on diets like this!). As the authors stress:

“Unlike vegetarian or vegan diets, plant-based diets assess the healthfulness of a dietary pattern consisting of foods primarily from plants without completely neglecting animal products. From a practical perspective, it is probably easier to shift the diet of populations towards a higher proportion of plant-based foods without excluding animal products.”

Plant-based dietary patterns and age-specific risk of multimorbidity of cancer and cardiometabolic diseases: a prospective analysis

The bottom line

I do my best to completely ignore online nutrition discourse, because 99 per cent of it is just too darn stupid to waste time on. However, I do occasionally – and very reluctantly – get pulled into it by clients and members of my EmpowerEd program, who ask for my feedback on videos and articles they’ve encountered. Most of these can be characterised by a monomaniacal focus on either one food or nutrient that the content creator asserts is the key to good health – protein, meat, fat (especially saturated fat), magnesium, vitamin D – or alternatively, one food or nutrient that is the cause of every disease known to humankind – ‘seed oils‘, ‘carbs‘, lectins, phytates, gluten, or whatever the bugaboo of the week happens to be.

But nutrition is so much more complex than this. As mentioned previously, all these macronutrients and micronutrients are embedded in a nutritional matrix. The question to ask is not “Am I eating too much carbohydrate?” but “What is my carbohydrate keeping company with – fibre, phytochemicals and plant protein, or sugar, extracted oils and food additives? Not “Am I getting enough protein?” but “What is my protein packaged with – fibre, phytochemicals and high-quality carbohydrates, or saturated fat and animal hormones?”

Once again, Michael Pollan may just have nailed it:

“Eat food. Not too much. Mostly plants.”

In Defense of Food

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1. Most of my readers will no doubt be either not from Australia, or too young to remember the Castrol Oil ad campaign from the 1980s, in which a mob boss and his mechanic repeatedly tangled over the right choice for engine oil. “Oils ain’t oils, Sol!” the mob boss admonishes the young buck who is trying to substitute an inferior product, meaning that not everything that appears similar, can perform the same functions. ↩︎
2. These 11 diseases were cancer (except for nonmelanoma skin cancer), type 2 diabetes, myocardial infarction, coronary artery bypass graft surgery or percutaneous transluminal coronary angioplasty, congestive heart failure, stroke, kidney failure, chronic obstructive pulmonary disease, Parkinson disease, multiple sclerosis, and amyotrophic lateral sclerosis. ↩︎