The Carb Report: Part 1

Part 1 of the Precision Nutrition Low Carb Diet Special Report…




Many people assume that carbohydrates are inherently fattening, due in part to the popularity of low carb diets like the Atkins diet.

You have probably heard at least one of the following reasons why:

  • Carbs spike your blood sugar and insulin, which causes fat gain
  • Carbs, especially sugar and grains, cause inflammation
  • Carbs are not essential in the diet like fat and protein

Let’s take a closer look…

Do carbs increase insulin levels?


Does increased insulin after meals lead to fat gain?

(Insulin is a satiety hormone – it makes you feel full and REFRAIN from eating.)

Are carbs inflammatory?

(Processed, like corn syrup? Probably. Whole grains? Not really.)

Are carbs less important that protein, fat, or the micronutrients that contribute to our health?

(Processed carbs – yes, they are less important. Whole, minimally processed carbs – different story.)

Can a low carb diet help people lose weight?

(Because it’s low in carbs? Maybe not.)

Can eating an appropriate amount of carbs help you look, feel, and perform your best?



The problem with not eating carbs

As a weight loss strategy, cutting carbs (while reducing the total number of calories consumed) works pretty well for a lot of people. If it didn’t Atkins would never have been popular in the first place.

However, carb reduction costs.

Most of us require some level of carbohydrates to function at our best over the long term.

We can cut carbs temporarily if we need to lose weight quickly. But, for most of us, keeping carbs too low for too long can have consequences. This is especially true for those who exercise.

If you are sedentary, your carb needs are lower. But if you like to work out regularly, restricting your car intake too drastically can:

  • decrease thyriod output
  • increase cortisol output
  • decrease testosterone
  • impair mood and cognitive function
  • catabolize muscle, and
  • suppress immune function.

READ: your metabolism might slow, your stress hormones go up, your muscle-building hormones go down. You can’t focus, feel sluggish and cranky, maybe even sick.




Your thyroid gland produces a hormone called T3. T3 is the most active thyroid hormone and is important for blood sugar management and proper metabolic function – aka maintain an appropriate metabolism.

Low T3 levels can lead to what is referred to as euthyroid sick syndrome – feeling constantly cold and sluggish. T3 is very sensitive to calorie and carbohydrate intake. When calories and carbs are too low, T3 levels drop. Another hormone, reverse T3 (rT3) is also sensitive to calorie and carb intake. rT3 inhibits T3.

Eating enough carbs can lower reverse T3. Not eating enough carbs will increase rT3 and block the sufficient production of T3.

Some research has shown that ketogenic (ultra-low carb) diets reduce T3 levels just as quickly as starvation would. Even when calories are held constant, reducing carbohydrates significantly reduces serum T3 levels (eating 25% the usual amount of carbs showed a 25% reduction in T3 levels).

Thyroid hormones are important for more than just metabolism and weight loss – they also affect overall health and energy levels.

So, if you aren’t eating enough and/or don’t eat enough carbs while training:

  • T3 decreases
  • reverse T3 increases, further blocking T3 production
  • you feel like crud and your training sucks

If you are active you need adequate energy and carbs for a healthy thyroid.



People who exercise regularly need to eat enough carbs or their testosterone decreases while their cortisol increases – a sure-fire recipe for muscle loss and fat gain.

This is also a marker for excessive training stress.

Research has continuously shown that inadequate carbohydrate intake can:

  • decrease testosterone (which no one wants, even females)
  • increase cortisol (which no one wants), and
  • negatively affect performance (which no one wants).



We have seen that eating too low-carb for too long can cause significant disruptions to many hormones. This seems especially true for women.

The hypothalamus and pituitary glands, found in the brain, are very sensitive to things like energy availability and stress (life and exercise included). These work together with other glands, such as the adrenals in what is known as the hypothalamic-pituitary-adrenal, or HPA, axis. The HPA axis regulates functions such as stress response, mood, digestion, immune system, libido, metabolism, and energy levels.

So, when women don’t eat enough calories or carbs, they may develop hypothalamic amenorrhea (HA). This means that the HPA axis’ perceived state of starvation or stress has caused absent or irregular periods. Hormone levels take a skydive and this is felt throughout the entire system – low levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, progesterone, and testosterone.

As discussed already, not eating enough carbs increases cortisol levels. Cortisol sends a signal to the HPA axis to further decrease pituitary activity.

Many women try to eat low-carb wanting to be healthier, yet these types of diets can significantly alter hormone production resulting in:

  • irregular or absent menstrual cycles
  • lowered fertility
  • low blood sugar and blood sugar swings
  • more body fat (especially around the waist and stomach)
  • loss of bone density
  • anxiety, depression, and other mental health issues
  • chronic inflammation and worsened chronic pain, and
  • chronic fatigue and disrupted sleep.

All Fruit Final


People usually think “protein” when they think about building muscle, but research shows that lowering carb intake can affect your muscle mass even when protein remains constant.

In one study out of the Netherlands comparing high carb (85%), moderate carb (44%), and low carb (2%) diets with equal amounts of protein (15% – an adequate amount, albeit a little low), the expected changes to T3 and reverse T3 hormones were observed – lowered amounts in the low-carb group and normal amounts in the high and moderate groups.

They also looked at urinary nitrogen excretion to see how the diets affected protein metabolism. The low carb diet increased muscle breakdown, due to the low carb intake lowering insulin levels.

Wait, I thought that higher insulin levels were always considered “bad”!?

ACTUALLY, insulin is crucial for building muscle – that is one of the reasons why enhanced bodybuilders include it in their protocols.

When you get enough carbs to meet your needs, you replenish muscle glycogen (storage form of glucose in the muscle) and create an anabolic (“building”) hormonal environment. On the opposite end, when you don’t get enough carbs, muscle glycogen is depleted and a catabolic environment is created = more protein breakdown, less protein synthesis.



Bottom line?

Not eating enough carbs can lower T3 levels, disrupt cortisol to testosterone ratios, interfere with a woman’s hormone balance, contribute to muscle loss, and prevent muscle gains.

But, wait! Aren’t low carb diets better for fat loss? And aren’t “fat-adapted” athletes performing just as well as athletes who eat a lot of carbs?

Low carbs are not better for fat loss

It’s true – many who try low carb diets are initially greeted with an immediate weight loss…


Also, research shows that, over the long term, any differences in fat loss between low carb and other diets even out.




Most studies that show low carb diets being superior usually fail to match protein intake between intervention groups. This means that the low carb group usually is consuming more protein than the higher carb groups.

Eating enough protein has several advantages:

  • protein has a higher thermic effect of food – the body has to use more energy to digest it (think, the “meat sweats”)
  • protein makes people feel fuller for longer, and
  • protein helps people retain lean muscle mass.

So, the secret to successful diets may be a high protein diet rather than a low carb diet.

Looking at a study where protein actually was matched, subjects who ate a moderate (40%) carb diet reported significantly better mood and lost about the same amount of weight as those on a ketogenic low carb (5%) diet. The moderate carb group actually showed a small tendency to lose more body fat than those on the low carb diet. Both groups improved insulin sensitivity while only the ketogenic group showed increased inflammatory biomarkers.

But, just to be sure, wouldn’t it be great to determine whether low carb diets work because they restrict carbs OR because they tend to increase protein? Someone did that!

Over the course of one year, researchers compared four groups:

  • normal protein, normal carb
  • normal protein, low carb
  • high protein, normal carb
  • high protein, low carb

And what did they find? Both high protein groups lost the most weight. So, varying levels of fats and carbs seems to make no difference to body composition.



Like most things, there is no “one-size-fits-all” model for carbohydrate requirements, such as in the bell curve diagram above.

The majority of the population does best with some carbs:

  • About 70% of people do really well with standard recommendations
  • Around 25% of people will do better by increasing or decreasing carbs slightly

A few people do best with high carbs:

  • Another 2.5% of people – maybe ultra-endurance athletes and a few other outliers – will thrive on very high amounts of carbs

A few people do best with low carbs:

  • Ketogenic diets are actually prescribed for some with epilepsy. There is also preliminary evidence that ketogenic diets benefits other neurological disorders, like Parkinson’s and Alzheimer’s
  • Very sedentary people and those who are extremely metabolically dysregulated (diabetes, metabolic syndrome) may benefit from a lower-carb diet for a while as part of an overall transition towards more activity and a healthier metabolism


While rare, even in athlete trials where most participants do better on high carb diets versus low carb diets, you will almost always find a few who perform better on an ultra-low-carb regime. However, individual responses vary enormously.

Each athlete – each person – is unique when it comes to carbohydrate requirements.

REMEMBER: MOST OF US ARE NOT ELITE ATHLETES, as much as you (gym goer, amateur physique competitor, CrossFit games qualifer) probably like to think of yourself as among those ranks.



Fad diets are mostly bad diets.

Low-fat, high-carb didn’t work for most of us. “Fat-free” high sugar treats left us feeling hungry and we ate a lot of rice cakes.

Then, we did a 180 and people jumped on the low-carb, high-fat bandwagon. Bring on the bacon! Unfortunately, for most of us, low carb doesn’t work for us either.

Strict diets don’t work

If your eating plan isn’t working for you, it’s tempting to make it more restrictive. If low carb isn’t making the fat melt off of you, then surely going full ketogenic will.

More restriction almost never works.

Unless you have extreme goals, don’t take your nutrition to extremes. Moderation is really the only sustainable method.

Most of us need some carbs

Most of us will look, feel, and perform at our best when we eat a reasonable, balanced amount of lean protein, healthy fats, and quality carbs.


You are unique. Your body is unique. Your individual carb requirements will depend on your goals, genetics, choice of carb source, and activity level. Adjust and experiment until you find the level that works best for you, or work with a coach to help you determine your optimal level.

SOURCE Low Carb Diet Special Report by Brian St. Pierre, MS, RD.

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