Too Little of a Good Thing: Carbohydrates

I was in charge of refreshments at a reception held for a guest lecturer and, aware of some of the attendees’ dietary limitations, selected gluten-free, sugar-free, dairy-free, and vegan cookies, as well as a large bowl of seasonal fruits.

“I am on the keto diet,” several of the guests told me as they avoided the cookies and fruit.

Where had I been?

I did not realize that the ketogenic diet had reappeared with such popularity, although I knew it never had really gone away since the days of Dr. Atkins. A few minutes on the internet made apparent the ubiquity of a diet that forces the body to switch from using glucose to fatty acids for energy. The diet seems to appeal to those who believe that total abstinence from sweet and starchy foods is the only way to control calorie intake. It also appeals to those who feel that carbohydrates are the source of physical and cognitive distress.

That adherence to such a diet has side effects ranging from unpleasant to worrisome is a small price to pay for those who follow a carbohydrate-free eating plan. Who cares about bad breath, constipation, “keto brain” (inability to concentrate and remember), difficulty sustaining strenuous exercise, and dangerously low electrolyte levels? As long as the weight comes off, it is worth it. Or so the thinking goes.

What happens after the diet ends can be dealt with after the diet ends, and if it seems impossible to maintain weight loss, well, why not go right back on the carbohydrate-free diet? Long-term effects? No one knows, so it could be good (or bad).

When someone is in ketosis, the body uses fat as a back-up energy system. Normally and naturally the body depends on glucose for all its energy needs. The glucose comes into the body as the end product of digestion of all carbohydrates, whether sucrose or brown rice, and is converted through a series of biochemical reactions into energy. In ketosis, the body uses fatty acids as its energy source. Once the body adapts to this alternate source of energy, it seems to run more or less the same (except for muscles which work longer and harder when using glucoose, the natural source of energy.) Exercise physiologists tell us that there is so little stored glucose in muscle on a carbohydrate-free diet, that muscles may fail to sustain strenuous movement after a few minutes of intense exercise. This means muscles used to sprint after a dog darting into the street, or a toddler about to climb up the rungs of a bookcase, will run out of energy reserves very quickly.

However, the body has a way of getting around the lack of carbohydrates for its glucose source by making its own. Certain amino acids in the protein we eat are converted to glucose in a process call gluconeogenesis. This occurs in the liver and kidneys and, according to advice given to wannabe ketotics, must be prevented. According to one Internet site, “Perfect Keto,” one should eat a specific ratio of fat to protein, because if too much protein and too little fat are consumed, the body will use the amino acids in protein as a source of self-made glucose. To prevent this, one should eat a very high fat diet, and only moderate amounts of protein, namely 75% fat, 20% protein, and a tiny amount of carbohydrate, 5%.

You will know whether or not you have achieved your goal of ketosis by testing levels of ketone bodies in your urine, blood or breath. Ketone bodies are three substances (acetoacetate, beta-hydroxybutyrate, and acetone) that the liver produces from fatty acids during periods of fasting, starvation, and very low or zero carbohydrate diets.

Although we tend to associate a carbohydrate-free or extremely low carbohydrate diet with dieting, it has long been seen as an effective treatment for controlling intractable pediatric epilepsy. Indeed, it is so important that the epileptic child not deviate from this diet that nutritional products have been developed containing flavored protein/fat liquid supplements that function as meal substitutes.

Moreover, avoiding carbohydrates used to be, prior to the availability of insulin, the only way someone with diabetes could handle this disease. And minimizing carbohydrate intake not only from sugary foods, but vegetables such as winter squash, corn on the cob, and carrots may help maintain a normal fasting blood sugar level.

Is it worth putting the body through a major physiological readjustment in order to lose weight?  What about the effect of carbohydrate deprivation on mood? Will there be any rebound eating of carbohydrates once the diet is switched back to including some carbohydrates? A definitive study comparing weight loss among 609 participants who were on a low carbohydrate or low-fat diet over a 12 month period was published this past winter in the Journal of the American Medical Association. The study did not support claims that avoiding carbohydrate produces a better weight-loss outcome. The difference in weight loss between the two groups was about l ½ pounds.

But perhaps the low carbohydrate diet is better for mood. Certainly anecdotal reports of the benefits of eliminating or drastically reducing carbohydrate intake would have you believe that clearer, sharper, focused, energetic minds result.  Here, also, the claim was not borne out by results of another twelve month study comparing  a low-fat and low-carbohydrate diet.

That moods improve among those in the study not denied carbohydrate is not surprising, assuming that some of the mood effects such as energy, focus, calmness and a sense of well-being are associated with normal serotonin activity. The absence of carbohydrate over prolonged periods of time prevents the amino acid tryptophan from entering the brain where it is converted to serotonin. The result: a decrease in serotonin levels and the risk of mood changes associated with too little of this neurotransmitter.

What happens if and when carbohydrates are added back into the diet? Diminished serotonin levels may make the dieter vulnerable to overeating this food group.

Next time I am asked to bring refreshments, I will be sure to include some pork rinds.

References

“Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss in Overweight Adults and the Association With Genotype Pattern or Insulin Secretion,”  The DIETFITS Randomized Clinical Trial,  Gardner, C., Trepanowski, J., DelGobbo, L., et al,  JAMA 2018; 319:667-679

Long-term effects of a Very Low-Carbohydrate Diet and a Low-Fat Diet on Mood and Cognitive  Function .Brinkeworth, G, Buckley J, Noakes, M,  Arch Intern Med 2009 :169; 1880-1873

“Influence of tryptophan and serotonin on mood and cognition with a possible role of the gut-brain axis,” Jenkins. T., Nguyen, J., Polglaze, K.,, et al, Nutrients 2016 8(1): 56.

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