[THE SEVEN] 2. Low-Carbohydrate, Metabolic-Flexibility Diet


THE SEVEN: Principles Of Nutrition For Slowing Biological Aging

This series is a distillation of our decades of researching, experimenting and generally obsessing over the question:

What is the ideal way to nourish a human body if the aim is to slow the progression of biological aging?

  1. Identify + Remove Dietary Allergens and Toxins
  2. The Low-Carbohydrate, Metabolic-Flexibility Diet
  3. How To Drink Water... Intelligently
  4. Reducing The Cognitive Overhead Of Eating Well (i.e. Staple Meals)
  5. Take Care Of Your (100 Trillion) Gut Bacteria
  6. Eating Nothing (i.e. Time-Restricted Eating)
  7. The Truly Essential Supplements

One of the most powerful nutritional “levers” we have to pull to improve the way our body feels and performs is the ratio of macronutrients - i.e. proteins, fats and carbohydrates - we put into it each day.

After experimenting with virtually every reasonable macronutrient ratio over the past decade (both on ourselves and with our clients), we’ve found one approach that produces the best results for nearly everyone: The Low-Carbohydrate, Metabolic-Flexibility Diet.

What is the low-carbohydrate, metabolic-flexibility diet?

There’s obviously a bit (ok, a lot) more nuance to the diet than this, but in its essence, the low-carb, metabolic-flexibility diet (LC/MF) is this:

1. Eating such that carbohydrates account for 25% (or less) of total calories.

(in combination with)

2. Time-restricted eating to build metabolic flexibility.

So there it is. Fairly simple on the surface, and in practice once you understand the nuances.

Ok, on to those nuances...

What is metabolic flexibility?

Metabolic Flexibility means your body is able to efficiently use both fats and carbs for energy, and switch between the two without suffering consequences.

This sounds like something we should all be able to do, but the reality is very few of us can actually do this.

Most people (even those on a typical low carb diet), are only able to use carbs efficiently, and struggle to use fats for energy. Keto folks have the opposite problem - they’ve trained their body to use fats efficiently, but in the process have lost the ability to use carbs for energy in a way that’s efficient and healthy.

The ideal state, we believe, is one in which your body can use either energy source, efficiently and on demand. Here’s why:

Why Low-Carb/Metabolic-Flexibility: The Benefits

The Fundamentals: Health Benefits

Stability Of Metabolic Energy (i.e. exiting the carbohydrate rollercoaster)

Improvements In Metabolic Markers Of Disease

Reduced Inflammation

Improved Mitochondrial Function

Ease Of Improving Body Composition

Improved Gut Health + Digestion

Accelerated Cellular Cleaning (Autophagy)

The elevator pitch for the Low-Carb/Metabolic-Flexibility diet is this:

Research shows that using exclusively fats for energy (i.e. ketosis) has a long list of metabolic benefits, but potentially some undesirable effects when done continuously for long periods.

It’s a similar story for carbohydrates. Using carbs for energy has unique benefits in specific applications, but similarly, potentially undesirable effects when done continuously.

The LC/MF diet aims to deliver the benefits of both approaches.

LC/MF provides many of the profound benefits of ketosis (albeit, to a lesser degree), but from a lifestyle that’s a world more flexible and easier to adhere to. It also allows for many of the unique benefits that can come from eating certain carbohydrates, something totally unavailable on a ketogenic diet.

And most importantly, LC/MF avoids the negative effects that almost always come with eating either way continuously.

Stability Of Metabolic Energy (i.e. exiting the carbohydrate rollercoaster)

When the body is running on carbohydrates exclusively, it’s essentially on a metabolic rollercoaster ride.

Within a couple hours following a carb-heavy meal, blood sugar rises dramatically. Insulin levels swiftly follow suit and rise as well, instructing cells to store this blood sugar (as glycogen or fat).

Sometime in the hours that follow, blood sugar will drop too low for the brain’s liking and it initiates a hormone cascade that leads to the secretion of cortisol (aka the stress hormone) and ghrelin (the hunger hormone). Predictably, you feel sluggish/hungry/grumpy and eat to fix the problem, starting the cycle all over again.

For most people, this is just “normal” and they’ve never really considered that there can be another way to fuel the body that is inherently more balanced and is largely absent of these ups and downs.

Once adapted to the LC/MF diet, the body is no longer so completely dependent on blood sugar for energy, as it can readily switch over to using fats (a much more stable energy source) when blood sugar levels drop. Any ups and downs in mood and energy are greatly reduced in magnitude and often disappear entirely.

Because the LC/MF diet includes a significant amount of carbohydrates (with dinner), stores of glycogen in our muscles and liver stay ‘topped off’ and provide an additional energy reserve for maintaining stability of metabolic energy, a unique advantage over a ketogenic diet.

Improvements In Metabolic Markers Of Disease

As blood sugar and insulin levels stabilize as the body adapts to LC/MF, a series of other hormones follow suit and similarly move towards a healthier, more balanced equilibrium.

A 2012 study was done on subjects following a diet in which carbohydrates are eaten primarily or exclusively at dinner (a diet functionally similar to, but considerably less effective than LC/MF). Over a 6 month period, the participants (on average) displayed the following changes (my notes in parenthesis):

“greater improvements in fasting glucose (blood sugar), average daily insulin concentrations, insulin resistance (a marker of pre-diabetes), low‐density lipoprotein cholesterol (LDL, correlated with heart disease), high‐density lipoprotein (HDL) cholesterol, C‐reactive protein (CRP, a marker of inflammation), tumor necrosis factor‐α (TNF‐α, another marker of inflammation), and interleukin‐6 (IL‐6, another marker of inflammation) levels.” [1]

Reduced Inflammation

As the study referenced in the section above shows, restricting carbohydrate consumption to a small window each day reduces levels of CRP, TNF‐α and IL-6 (all markers of inflammation).

There is good evidence that this effect will be even more pronounced with LC/MF, as the body will be using fats for energy at a significantly higher rate, meaning circulating levels of β-hydroxybutyrate (BHB, a ketone byproduct of fat breakdown) will be higher on average.

BHB has been shown to suppress activation of one of the body’s primary pro-inflammatory pathways, known as the NLRP3 inflammasome. [2]

Improved Mitochondrial Function

Our mitochondria are our cellular power plants, using ketones or glucose to produce ATP (which powers essentially everything the cell does).

As our mitochondria get healthier and more efficient, so too do countless downstream metabolic processes, and we typically experience the net effect of this as “having more energy”.

Using fats for energy (which the body will do more frequently with LC/MF) has been shown to increase mitochondrial efficiency relative to glucose metabolism, and increase the production of new mitochondria (mitochondrial biogenesis). [3]

Ease Of Improving Body Composition

The two biggest obstacles most people face in an effort to move towards a leaner body composition are (1) hunger and (2) metabolic inability to ‘burn’ body fat efficiently. LC/MF addresses both.

By stabilizing blood sugar and insulin levels, LC/MF significantly reduces the frequency and intensity of experiences of “hunger” (which, again, is just the brain’s hormonal response to a drop in blood sugar). When hunger isn’t skewing our decision-making process several times each day, it’s a world easier to make better decisions about when, what and how much we eat.

LC/MF also trains our body to burn fat more efficiently, and body fat will be used for energy at a higher rate if you choose to calorie-restrict in an effort to move towards a leaner body composition.

Improved Gut Health + Digestion

LC/MF prioritizes getting a diversity of indigestible fibers and starches in the diet, which is arguably the #1 key to building and maintaining a robust, healthy microbiome (which is the #1 key to improving gut health and digestion).

I mention this here because it comes in contrast to a ketogenic diet, which is often deficient in these valuable fibers and starches.

Accelerated Cellular Cleaning (Autophagy)

Autophagy is our cells’ primary process of recycling unneeded or degraded proteins and organelles. The greater the rate and frequency with which autophagy is running, the more likely our cells (and thus, the tissues and organs constituted by them) are to be healthy and live longer.

The primary mechanism for up-regulating autophagy? Time restricted eating, a core element of LC/MF. [4]

How to eat for Metabolic Flexibility: Implementation

The Fundamentals:  Implementation

Less than 25% of daily calories come from carbohydrates

55-65% of daily calories come from healthy fats

10-20% of daily calories come from protein

Modified Intermittent Fasting for 15+ hours in every 24hr period

Very-Low or No-Carb before dinner

Occasional high carb days are OK! (but not more than 1 per week)

1. Getting Your Macronutrients Right

Macronutrient ratios (i.e. carbs-fats-proteins) are the core of LC/MF, and the whole thing only “works” when you consistently stay in the ranges outlined below.

Realistically, when you’re starting to eat this way, you’re going to need to weigh your foods (I use this pocket scale) and record them in a diet tracking app that calculates the macronutrients (like My Fitness Pal). Without this, you risk dramatically overshooting your targets and being left wondering why you’re not experiencing all those benefits mentioned in the sections above.

After a month or two of weighing your foods and seeing the macronutrients of each, you’ll gain a better intuitive sense of the macronutrients in the foods you’re eating, and need to weigh and record your foods less frequently. (This is made even easier when you use a Staple Meals approach to meal prep, as we’ll outline in the 4th installment in this series)

Less than 25% of daily calories come from carbohydrates.

The most important component of the Metabolic Flexibility diet is keeping daily carbohydrate intake at less than 25% of your total calories. That means:

For a 2000 calorie/day diet = Less than 125g carbs per day
2500 calories = Less than 156g carbs per day
3000 calories = Less than 187g carbs per day

55-65% of daily calories come from healthy fats.

Limiting carbohydrates alone won’t get you to Metabolic Flexibility and its benefits - it’s also necessary to get plenty of healthy, easily digestible fats in your diet to give your body fuel for fat-burning periods of the day.

Coconut oil, grass-fed butter, ghee, and ideally MCTs (like Ketobasis) are the best examples of clean, easily-utilized fats that get used for energy preferentially, rather than stored. A minimum of half of your fats in a given day should come from these sources.

For a 2000 calorie/day diet = 122-144g fats per day
2500 calories = 153-181g fats per day
3000 calories = 183-217g fats per day

10-20% of daily calories come from protein.

Protein supplies the building blocks for maintaining and building our muscles, an important process to support even if you don’t have aspirations of building muscle.

Muscle is the body’s primary consumer of fat stores, so even if your aim is to lose weight, supporting your lean mass is essential, and 10% of your daily calories from protein will be plenty for this. If you’re looking to add muscle, or you train intensely in any discipline, you’ll do best staying towards the upper end of this range.

For a 2000 calorie/day diet = 50-100g protein per day
2500 calories = 63-125g protein per day
3000 calories = 75-150g protein per day

2. Time Restricted Eating

The macronutrient ratios above are essentially an ordinary low-carbohydrate diet. So what makes this a Metabolic Flexibility diet? Time restricted eating, of course.

Time restricted eating is to intentionally eat only with a certain time window each day (and thus, fasting for the remainder of the 24 hour period).

When we’re sleeping we’re (hopefully) not eating, so this effectively amounts to tacking a short-ish fasting period onto each end of your daily time in bed.

These daily fasting periods serve several critical functions; giving your digestive system a pause, improving hydration and - most importantly - sending your body a strong signal to start utilizing stored glycogen and body fat for energy.

I promise this is much easier than it might look at first glance, and once you get used to it, it becomes hard to imagine not giving your body this break from food each day.

Modified Intermittent Fasting for 15+ hours in every 24hr period.

In my experience, 15 hours is the minimum daily fasting period that communicates to the body that it needs to start efficiently utilizing stored fat for energy. Something closer to 16-18 hours is probably the ideal, and what I do most days.

15 hours is easier than it might sound; this could mean finishing dinner at 8pm and then eating your first calories at 11am the day following.

The “modified” part of this protocol makes it even easier to adhere to. Consuming a few hundred calories of easily digested fats like ghee, coconut oil and MCTs doesn’t meaningfully disrupt the metabolic signal-sending we’re after, but it does make the fasting period more pleasurable.

I usually do this via my late-morning matcha lattes.

4oz Almond Milk
6oz Boiling Water
2tsp (3g) Matcha Powder
2 Scoops (10g) Ketobasis MCTs
1Tbsp (13g) Grass Fed Ghee

Directions: Add contents to a jar or blender, shake/blend. Enjoy.

That’s 23g/207cal of clean, easily utilized fats that keep my energy levels up and my brain sharp for the duration of the modified fasting period (and it’s considerably yummier than any cafe-bought matcha latte I’ve ever had).

3. Very-Low to No Carbs Before Dinner

As you finish your modified fasting period, your body will be deriving a significant portion of its metabolic energy from fats, which is exactly what we’re aiming for.

The foods you chose to eat at the conclusion of your fasting period are crucial, as they can either continue to support this process or end it prematurely. Ideally, anything you eat between this point and dinner should have as few carbohydrates as possible.

A salad or roasted green vegetables accompanied by some form of clean protein is a good afternoon meal that fits these criteria. Our upcoming articles on The Staple Meals Philosophy will have dozens more ideas that can also be built to have next-to-no carbohydrates.

I personally have a shake (Genesis + Ketobasis in homemade almond milk) as my mid-afternoon ‘meal”, but I’m well aware this is not for everyone. :)

4. Occasional High Carb Days Are OK! (but not more than 1 per week)

We’re all human, and in my experience, it’s psychologically valuable to diverge from our patterns on occasion.

Thankfully, the LC/MF diet allows for this.

Having a day every now and then when you eat way more carbs than the diet typically allows won’t undo the work you’ve done to adapt to this way of eating, or the health benefits it’s bestowed.

Your fasting period the following day might not feel quite as smooth as usual as your blood sugar and hormone levels re-stabilize, but none of the core metabolic adaptations you’ve worked for will be meaningfully diminished.

5. Adapting To LC/MF

For most people, LC/MF will be fairly different from their previous ways of eating, and the body will need a bit of time to adapt, particularly in balancing blood sugar levels and building the metabolic pathways needed to utilize fat for energy efficiently.

This adaptation time will be different for everyone, but it generally falls somewhere in the range of 3 to 8 weeks before it “clicks” such that the benefits are obvious. I highly recommend being diligent about adhering to your macronutrient targets and modified fasting periods during the first 4 or 6 weeks, as it’s easy to throw the whole project off course and never get to the point where you’re reaping the rewards of your efforts (this means no high-carb days until at least your 5th week).


[1] https://onlinelibrary.wiley.com/doi/full/10.1038/oby.2011.48

[2] https://www.nature.com/articles/nm.3804

[3] https://www.frontiersin.org/articles/10.3389/fnmol.2017.00377/full

[4] http://www.tandfonline.com/doi/full/10.4161/auto.6.6.12376

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