And The Brain Goes Marching On!

In Tuesday’s newsletter, we asked you “when does the human brain stop developing?” and got the above-depicted, below-described, set of responses:

• About 64% of people said “Never”
• About 16% of people said “25 years”
• About 9% of people said “65 years”
• About 5% of people said “13 years”
• About 3% of people said “18 years”
• About 3% of people said “45 years”

Some thoughts, before we get into the science:

An alternative wording for the original question was “when does the human brain finish developing”; the meaning is the same but the feeling is slightly different:

• “When does the human brain stop developing?” focuses attention on the idea of cessation, and will skew responses to later ages
• When does the human brain finish developing?” focuses on attention on a kind of “is it done yet?” and will skew responses to earlier ages

Ultimately, since we had to chose one word or another, we picked the shortest one, but it would have been interesting if we could have done an A/B test, and asked half one way, and half the other way!

Why we picked those ages

We picked those ages as poll options for reasons people might be drawn to them:

• 13 years: in English-speaking cultures, an important milestone of entering adolescence (note that the concept of a “teenager” is not precisely universal as most languages do not have “-teen” numbers in the same way; the concept of “adolescent” may thus be tied to other milestones)
• 18 years: age of legal majority in N. America and many other places
• 25 years: age popularly believed to be when the brain is finished developing, due to a study that we’ll talk about shortly (we guess that’s why there’s a spike in our results for this, too!)
• 45 years: age where many midlife hormonal changes occur, and many professionals are considered to have peaked in competence and start looking towards retirement
• 65 years: age considered “senior” in much of N. America and many other places, as well as the cut-off and/or starting point for a lot of medical research

Notice, therefore, how a lot of things are coming from places they really shouldn’t. For example, because there are many studies saying “n% of people over 65 get Alzheimer’s” or “n% of people over 65 get age-related cognitive decline”, etc, 65 becomes the age where we start expecting this—because of an arbitrary human choice of where to draw the cut-off for the study enrollment!

Similarly, we may look at common ages of legal majority, or retirement pensions, and assume “well it must be for a good reason”, and dear reader, those reasons are more often economically motivated than they are biologically reasoned.

So, what does the science say?

Our brains are never finished developing: True or False?

True! If we define “finished developing” as “we cease doing neurogenesis and neuroplasticity is no longer in effect”.

Glossary:

• Neurogenesis: the process of creating new brain cells
• Neuroplasticity: the process of the brain adapting to changes by essentially rebuilding itself to suit our perceived current needs

We say “perceived” because sometimes neuroplasticity can do very unhelpful things to us (e.g: psychological trauma, or even just bad habits), but on a biological level, it is always doing its best to serve our overall success as an organism.

For a long time it was thought that we don’t do neurogenesis at all as adults, but this was found to be untrue:

How To Grow New Brain Cells (At Any Age)

Summary of conclusions of the above: we’re all growing new brain cells at every age, even if we be in our 80s and with Alzheimer’s disease, but there are things we can do to enhance our neurogenic potential along the way.

Neuroplasticity will always be somewhat enhanced by neurogenesis (after all, new neurons get given jobs to do), and we reviewed a great book about the marvels of neuroplasticity including in older age:

The Brain’s Way of Healing: Remarkable Discoveries and Recoveries from the Frontiers of Neuroplasticity – by Dr. Norman Doidge

Our brains are still developing up to the age of 25: True or False?

True! And then it keeps on developing after that, too. Now this is abundantly obvious considering what we just talked about, but see what a difference the phrasing makes? Now it makes it sound like it stops at 25, which this statement doesn’t claim at all—it only speaks for the time up to that age.

A lot of the popular press about “the brain isn’t fully mature until the age of 25” stems from a 2006 study that found:

❝For instance, frontal gray matter volume peaks at about age 11.0 years in girls and 12.1 years in boys, whereas temporal gray matter volume peaks at about age at 16.7 years in girls and 16.2 years in boys. The dorsal lateral prefrontal cortex, important for controlling impulses, is among the latest brain regions to mature without reaching adult dimensions until the early 20s.❞

~ Dr. Jay Giedd

Source: Structural Magnetic Resonance Imaging of the Adolescent Brain

There are several things to note here:

• The above statement is talking about the physical size of the brain growing
• Nowhere does he say “and stops developing at 25”

However… The study only looked at brains up to the age of 25. After that, they stopped looking, because the study was about “the adolescent brain” so there has to be a cut-off somewhere, and that was the cut-off they chose.

This is the equivalent of saying “it didn’t stop raining until four o’clock” when the reality is that four o’clock is simply when you gave up on checking.

The study didn’t misrepresent this, by the way, but the popular press did!

Another 2012 study looked at various metrics of brain development, and found:

• Synapse overproduction into the teens
• Cortex pruning into the late 20s
• Prefrontal pruning into middle age at least (they stopped looking)
• Myelination beyond middle age (they stopped looking)

Source: Experience and the developing prefrontal cortex ← _{^{check out figure 1, and make sure you’re looking at the human data not the rat data}}

So how’s the most recent research looking?

Here’s a 2022 study that looked at 123,984 brain scans spanning the age range from mid-gestation to 100 postnatal years, and as you can see from its own figure 1… Most (if not all) brain-things keep growing for life, even though most slow down at some point, they don’t stop:

Brain charts for the human lifespan ← _{^{check out figure 1; don’t get too excited about the ventricular volume column as that is basically “brain that isn’t being a brain”. Do get excited about the rest, though!}}

Want to know how not to get caught out by science being misrepresented by the popular press? Check out:

How Science News Outlets Can Lie To You (Yes, Even If They Cite Studies!)

Take care!

Carb-Strong or Carb-Wrong?

We asked you for your health-related view of carbs, and got the above-depicted, below-described, set of responses

• About 48% said “Some carbs are beneficial; others are detrimental”
• About 27% said “Carbs are a critical source of energy, and safer than fats”
• About 18% said “A low-carb diet is best for overall health (and a carb is a carb)”
• About 7% said “We do not need carbs to live; a carnivore diet is viable”

But what does the science say?

Carbs are a critical source of energy, and safer than fats: True or False?

True and False, respectively! That is: they are a critical source of energy, and carbs and fats both have an important place in our diet.

❝Diets that focus too heavily on a single macronutrient, whether extreme protein, carbohydrate, or fat intake, may adversely impact health.❞

~ Dr. Russel de Souza et al.

Source: Low carb or high carb? Everything in moderation … until further notice

(the aforementioned lead author Dr. de Souza, by the way, served as an external advisor to the World Health Organization’s Nutrition Guidelines Advisory Committee)

Some carbs are beneficial; others are detrimental: True or False?

True! Glycemic index is important here. There’s a big difference between eating a raw carrot and drinking high-fructose corn syrup:

Which Sugars Are Healthier, And Which Are Just The Same?

While some say grains and/or starchy vegetables are bad, best current science recommends:

• Eat some whole grains regularly, but they should not be the main bulk of your meal (non-wheat grains are generally better)
• Starchy vegetables are not a critical food group, but in moderation they are fine.

To this end, the Mediterranean Diet is the current gold standard of healthful eating, per general scientific consensus:

• The Mediterranean Diet: What Is It Good For?
• Four Ways To Upgrade The Mediterranean Diet

A low-carb diet is best for overall health (and a carb is a carb): True or False?

True-ish and False, respectively. We covered the “a carb is a carb” falsehood earlier, so we’ll look at “a low-carb diet is best”.

Simply put: it can be. One of the biggest problems facing the low-carb diet though is that adherence tends to be poor—that is to say, people crave their carby comfort foods and eat more carbs again. As for the efficacy of a low-carb diet in the context of goals such as weight loss and glycemic control, the evidence is mixed:

❝There is probably little to no difference in weight reduction and changes in cardiovascular risk factors up to two years’ follow-up, when overweight and obese participants without and with T2DM are randomised to either low-carbohydrate or balanced-carbohydrate weight-reducing diets❞

~ Dr. Celeste Naud et al.

Source: Low-carbohydrate versus balanced-carbohydrate diets for reducing weight and cardiovascular risk

❝On the basis of moderate to low certainty evidence, patients adhering to an LCD for six months may experience remission of diabetes without adverse consequences.

Limitations include continued debate around what constitutes remission of diabetes, as well as the efficacy, safety, and dietary satisfaction of longer term LCDs❞

~ Dr. Joshua Goldenberg et al.

Source: Efficacy and safety of low and very low carbohydrate diets for type 2 diabetes remission

❝There should be no “one-size-fits-all” eating pattern for different patient´s profiles with diabetes.

It is clinically complex to suggest an ideal percentage of calories from carbohydrates, protein and lipids recommended for all patients with diabetes.❞

~Dr. Adriana Sousa et al.

Source: Current Evidence Regarding Low-carb Diets for The Metabolic Control of Type-2 Diabetes

We do not need carbs to live; a carnivore diet is viable: True or False?

False. For a simple explanation:

The Carnivore Diet: Can You Have Too Much Meat?

There isn’t a lot of science studying the effects of consuming no plant products, largely because such a study, if anything other than observational population studies, would be unethical. Observational population studies, meanwhile, are not practical because there are so few people who try this, and those who do, do not persist after their first few hospitalizations.

Putting aside the “Carnivore Diet” as a dangerous unscientific fad, if you are inclined to meat-eating, there is some merit to the Paleo Diet, at least for short-term weight loss even if not necessarily long-term health:

What’s The Real Deal With The Paleo Diet?

For longer-term health, we refer you back up to the aforementioned Mediterranean Diet.

Enjoy!