Ask almost anyone what they need to do to lose a few pounds, and theyll probably say:Cut back on the carbs.As a nutrition coach, Ive heard it hundreds of times.
While the low carb movement has waxed and waned in popularity since theAtkinsrevival of the late 90s and early 2000s, most folks now assume that carbohydrates are inherently fattening.
Health-conscious diners order bunless hamburgers, skip the baked potato side dish, and send the bread basket back to the kitchen. (Or dont, and feel guilty about it.)
In the past few years, Ill bet youve heard (or thought) at least one of the following:
Seems simple and logical. Which is the problem.
These simplistic statements about good foods and bad foods ignore biological complexity and the bigger picture.
Lets look closer.
Yes, they do.
No.
(Insulins actually a satiety hormone in other words, it makes you feel full so the idea that on its own it leads to fat gain doesnt make sense.)
That depends. Are we talking about processed corn syrup? Probably.
But if were talking about whole grains, not really.
Well, if youre talking about processed carbs, the answer is a resounding yes.
But if youre talking about whole, minimally processed carbs, thats a different story.
Of course it can.
Is it because it is low in carbs?
Maybe. Maybe not.
You bet it can.
As a weight loss strategy, cutting carbs (while reducing the total number of calories) clearly works pretty well for some people.If it didnt, then Atkins would have never been popular in the first place.
Heres the thing, though: Carb reduction costs us.
You see, most of us require some level of carbohydrates to function at our best over the long term.
Sure, 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 disastrous consequences.
This is especially true for those of us who work out.
If youre sedentary, your carb needs are lower. So you might be able to get away with more restriction.
But if you like to exercise regularly and enthusiastically, restricting your carb intake too drastically can lead to:
In other words: Your metabolism might slow, your stress hormones go up and your muscle-building hormones go down.
You feel lousy, spaced-out, sluggish, cranky and maybe even sick.
Most vexing of all: You probably dont even lose that much weight in the long term.
If youre interested in the details and some research, read on. If you just want to know what to do, skip to the end.
In order to function properly and to maintain an appropriate metabolism, our body produces an important hormone called T3.T3 is the most active thyroid hormone and is incredibly important for blood glucose management and proper metabolic function.
Low T3 levels can lead to a condition called euthyroid sick syndrome, in which people are constantly cold and sluggish. (Imagine your metabolic body motor idling at a slower speed.)
A landmark study, known as the Vermont Study, found that T3 is very sensitive to calorie and carbohydrate intake. When calories and carbs are too low, your T3 levels drop.
In addition, the Vermont Study found that another hormone,reverse T3 (rT3), is also sensitive to calorie and carbohydrate intake. Reverse T3, as the name implies, inhibits T3.
Getting enough carbs can lower reverse T3. Not eating enough carbs will increase it, thus blocking the important work of T3.
The Vermont Study is far from alone. Other research confirms that ketogenic (ultra-low carb) diets reduce T3 levels as rapidly as starvation.
Additional studies show that when calories are held constant (in this case at 2100 calories), reducing carbohydrates from 409 g to 202 g and then to 104 g significantly reduced serum T3 levels (from 91 to 86 to 69 ng/dL respectively).
Finally, French researchers examined four calorically equal diets (2800 calories in this case), lasting 1 week each. Two of these diets contained 250 grams of carbs, which is a fairly typical proportion. The low-carb diet included 71 grams of carbs, and the high-carb diet included 533 grams of carbs.
T3 levels were equal on the normal and high carb diets (ranging from 163.3 to 169.5 ng/100 mL). However, on the low carb diet they fell to 148.6 ng/100 mL on average. And of course, rT3 correspondingly rose on the low carb diet, but not on the standard or high carb diets.
Thyroid hormones are important for more than just weight loss; they also have profound effects on our overall health and energy levels.
Thus, when you dont eat enough, and/or eat enough carbs while training:
If youre active, youneed adequate energy and carb intakes for a healthy thyroid.
Research consistently shows that people who exercise regularly need to eat enough carbs or their testosterone will fall while their cortisol levels rise. This is a sure-fire recipe for losing muscle and gaining fat.
Incidentally, its also a marker for excessive training stress.
In a study in Life Sciences, men who ate a high carbohydrate versus a low carbohydrate diet for 10 days had higher levels of testosterone and sex hormone binding globulin, and lower levels of cortisol.
A few years later, another study took this research a step further. This time the subjects included men and women who exercised regularly. And in addition to considering the effect of their diet on hormones, researchers put them through some performance tests.
Once again, when the subjects ate a low carb diet, their testosterone (and other anabolic hormones) went down, while their cortisol went up.
And, after following a low carb diet for just three days, only two of the six participants were able to complete the cycling test! Meanwhile, when following the higher carb diet for three days, all six participants were able to complete the test.
In 2010, researchers reconsidered the same question this time in relation to intense exercise. In this particular study, subjects eating the low carb diet (where 30% of their calories came from carbs) saw a drop of 43% in their testosterone to cortisol ratio. Not good. Meanwhile, the control group (who got 60% of their calories from carbs) saw no change in their testosterone/ cortisol ratios.
Thus:
We now know that eating too low-carb for too long can cause significant disruptions to many hormones.
This seems especially true for women, whose bodies may be more sensitive than mens to low energy or carbohydrate availability (perhaps because of the evolutionary importance of having enough body fat and nutrients to sustain a pregnancy).
While organs like our gonads or thyroid make hormones, Mission Control of our hormone production system is the central nervous system (CNS), i.e. the brain.
Our hypothalamus and pituitary glands, which sit in the brain, are exquisitely sensitive to things like energy availability and stress (which can include life stress and exercise stress).
The hypothalamus and pituitary work together with other glands such as the adrenal glands. This partnership is often known as the hypothalamic-pituitary-adrenal, orHPA, axis.
Thus, when women dont eat enough calories or carbohydrate or even when women eat enough calories but not enough carbohydrate they face hypothalamic amenorrhea.
This means disrupted hormones and stopped or irregular periods because of the HPAs response to perceived starvation and stress.
In hypothalamic amenorrhea, hormone levels plummet, and the cascade is felt throughout the system. You end up with low levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, progesterone, and testosterone.
In addition, weve already seen that not eating enough carbohydrate tends to increase cortisol levels. When cortisol rises, it signals your HPA axis to further decrease pituitary activity. Not good.
Your HPA axis regulates functions such as stress response, mood, digestion, immune system, libido, metabolism and energy levels.
And your pituitary in particular is responsible for synthesizing and secreting growth hormone, thyroid stimulating hormone, prolactin, LH, FSH and other incredibly important hormones.
With all this said, heres the takeaway message: Many women try to eat low-carb, wanting to be healthier.
Yet because low-carb diets can significantly disrupt hormone production, women with too-low carb intakes especially active women can face:
ironically, this is the exact opposite of what they wanted in the first place.
When we think about building muscle, we usually think of protein. But research shows that lowering carb intake can affect your muscle mass even if protein remained constant.
In other words, even if youre guzzling protein shakes or eating steak 5 times a day, you could be losing muscle if you arent getting enough carbs.
A recent study from the Netherlands compared three diets:
All diets had the same total calories and the same amount of protein 15%. (Yes, a little low, but more or less adequate.)
The result? For starters, pretty consistent with other research.
But heres the interesting wrinkle. In this study, the researchers also measured urinary nitrogen excretion to see how the diets affected protein breakdown.
In this case,the low carb dietincreasedmuscle breakdown, because severely low carbs lowered insulin levels.
Again, youd assume that protein intake would determine muscle breakdown. And you might assume based on what youve heard that having higher insulin is always bad.
In fact, insulin is crucial for building muscle.
When you get enough carbs to meet your needs, you replenish muscle glycogen and create an anabolic (building-up) hormonal environment. You get strong and buff. Thats good.
Conversely, when you dont eat enough carbohydrate, muscle glycogen is depleted and a catabolic (breaking-down) hormonal environment is created, whichmeansmore protein breakdown and less protein synthesis. This means slower muscle growth or even muscle loss.
The bottom line? Not eating enough carbohydrates can lower T3 levels, disrupt cortisol to testosterone ratios, interfere with a womans delicate hormone balance, contribute to muscle loss, and prevent muscle gains.
Definitely not what most of us want!
But wait a minute.
Even if all of this is true, arent low carb diets better for fat loss?
And arent fat-adapted athletes performing just as well as athletes who eat a lot of carbs?
The logic seems so clear and appealing: High carbs lead to insulin which leads to fat storage. Low carbs keep insulin low, which should get you effortlessly lean while you enjoy chicken wings, salmon, eggs, and butter.
Indeed, many people who try low-carb dieting are initially pleased by an immediate weight loss which is mostly water and glycogen. So, in the short term, itseems like low-carb diets are superior.
But does long-term evidence support low-carb dieting?
Research says no. Over the long haul, any differences between low-carb and other diets even out.
Most studies that suggest low-carb diets are superior suffer from a common methodological flaw: They usually dont match protein intake between groups. This means that the low carb group often ends up consuming significantly more protein.
We know that getting plenty of protein has many advantages:
In other words, the big secret might be a high protein diet rather than a low carb diet.
So lets play fair and look ata study where protein was matched. In this study,subjects who ate a moderate carb diet (40% calories from carbs) reported significantly better mood, and lost about the same amount of weight as those on a ketogenic low-carb diet (5% calories from carbs).
Actually, the group who ate a moderate amount of carbs showed a small (though not statistically significant) tendency to lose more body fat as compared to those on a low carb diet (5.5 kg vs 3.4 kg in 6 weeks).
Both diets improved insulin sensitivity. However, the ketogenic diet also increased LDL cholesterol and inflammatory markers and subjects who were on it felt less energetic.
Thus, in this study:
Makes you wonder why low carb gets so much hype, doesnt it?
Especially considering that a recent review of long-term low carb versus low fat diets the largest of its kind so far found that both low carb and low fat diets reduced peoples weight and improved their metabolic risk factors.
In this review, both diets had about the same weight loss, changes in waist circumference, and measurements of several metabolic risk factors (blood pressure, blood glucose, insulin).
Still, it would be great to understand more about what makes low carb diets work at all. One recent study asked:Do low carb diets work because they restrict carbs or because they tend to increase protein?
Over the course of one year, the researchers compared four different conditions:
Interestingly, the two groups eating the high protein lost the most weight.
And the real kicker? Varying the levels of fats and carbs seemed to make no difference to body composition.
As our name implies, at Precision Nutrition we dont believe in one-size-fits-all dietary recommendations.
Like most things, carbohydrate requirements fall on a bell curve.
See the original post:
Carb controversy: Why low-carb diets have got it all wrong ...
