The Good And Bad of Low Carb Diets

Low carb diets, such as Atkins, South Beach, Paleo/Caveman Diets,  are the rage these days.   Today, I’d like to investigate the data in terms of how effective these diets are, as well as the question of how safe they are.

Low carb diets are characterized by a drastic reduction in carbohydrate intake such as the elimination of rice, bread, juice, sugar, pasta, starchy vegetables. 

Because carbohydrate intake is greatly reduced, these diets put an emphasis on eating more protein and/or fat rich foods such as meats, chicken, fish, certain cheeses.  In response to early criticism of being meat-centric and being unhealthy, newer versions of these diets have started to emphasize the inclusion of  certain vegetables and fruits that have negligible amounts of carbohydrates. 

These diets work by depriving the body of carbohydrates which are a main fuel of the body, thereby forcing the body to use fats and/or protein as fuel sources.  Ketones are a by-product of this metabolic switch.  

These diets work partly by changing the body’s hormonal reaction to food intake.  For example, if you don’t eat a lot of carbohydrates, you diminish the body’s production of insulin.  Insulin is a hormone that allows the body to store excess calories in muscles and fat tissue (e.g. belly fat or butt fat).

Perhaps for safety reasons, low carb diets are not done

for a long time or done indefinitely.  The prototype of a low carb diet such as Atkins divides the program into phases—called the induction phase, maintenance, and ongoing.  The induction phase is the strictest and carbohydrate restriction is limited to 13-20 (depends on which study you read). The induction phase is so-called because the goal of strict carbohydrate restriction is to induce ketosis—where the body starts to use fat as fuel.  Over time, as one goes through the maintenance and ongoing phases, the amount of carbohydrates allowed increases.

Reviewing available data, the low carb diet has several strengths but also some safety concerns. 

First, at least seven studies show that low carb diets are effective and in fact, produce faster results versus a low fat diet, at least for the first 3-6 months.  As long as one sticks to the low fat diet, you start to get the same results between the low carb and low fat diet after about a year.   This is a meaningful benefit for someone who wants to get results sooner because they have a target date in mind, or perhaps seeing results sooner makes them more motivated and allows them to stick to the diet better. 

A significant portion of the weight that is lost initially with the low carb diet is actually water weight as opposed to fat weight.  This is because glycogen, which is a stored form of energy that the body uses when it is deprived of carbohydrates contains a lot of water.  When the body starts to use glycogen, the water attached to the glycogen is released via urine.   The flip side to this phenomenon is that when one stops the diet before they start to lose the fat weight, it is very easy to gain back the water weight because the body quickly restores glycogen stores once it has access to carbohydrates.

Second,  a low carb diet seems to increase our metabolism the most.  A study recently published by the Journal of the American Association showed that when people ate a low carb diet, they burn about 300 calories more throughout the day than when they ate a low fat or low glycemic index diet.  In other words,  just by being on a low carb diet, you increase your metabolism and burn more calories without doing anything extra.  300 calories is equivalent to about one hour of moderate exercise such as jogging.   This is significant because I don’t know many people who jog for one hour seven days a week.  

We do not know exactly what causes this increase in metabolism.  One hypothesis is that perhaps the body just needs to use more energy to digest a low carb diet, or to digest the extra protein and fat.    What the scientists also observed was that people’s hormonal balance changes depending on the type of diet they ate.  These observations are preliminary and do not conclusively explain this phenomenon. 

Anecdotally, I would say that people doing the low carb diet say they seem to have more energy and feel better overall and are not suffering as much from the diet—I wonder if this is because of the increased metabolism that scientists have now confirmed in this study.

Third, multiple studies show that people who follow a low carb diet tend to stick with them better.  In other words, a low carb diet might be easier to do overall.  Protein and fat are known to be more satiating than carbohydrates (people feel more satisfied when eating these molecules), and they are also slower to digest so perhaps people feel less hungry for longer periods of time when they are on a low carb diet vs. a low fat diet.

Surprisingly, a low carb diet does not seem to increase cholesterol or triglyceride levels despite higher intake of protein and fats.  On the contrary, it seems to be better than a low fat diet at improving or reducing those markers.  Although this improvement in cholesterol and triglycerides have been shown in several studies, we should note that these studies are relatively short term (less than a year), and so we still do not know the long term effects of  low carb, high protein, high fat diet on cardiovascular health. 

One safety issue that frequently comes up for low carb diets is ketoacidosis or the production of too many ketones.  Ketones are produced when the body starts to burn fat because of carbohydrate deprivation.  This is a natural phenomenon and having some amount of ketones in the body is usually not problematic. 

However, when ketone levels are too high—ketoacidosis happens.  The symptoms are a sudden onset of lethargy, nausea, vomiting, breathing changes,  weakness and sometimes an acetone smelling breath.  I have not come across a study which says how often this problem occurs.  In the multiple low carb studies I have examined, the authors have not reported cases of ketoacidosis from low carb diet in their studies.  This makes one think that this is a relatively rare phenomenon in the context of low carb diets.

For my patients who are recommended a low carb diet, I would usually do a blood test to make sure they don’t have diabetes, liver and kidney disease, and metabolic imbalances as a low carb diet may not be compatible for them. I will also monitor these patients regularly to make sure that they are healthy and are doing okay.

Lastly, the same study which showed that a low carb diet can increase metabolism also showed some cautionary markers.  Specifically, they found that persons doing a low carb diet tend to have higher levels of cortisol, a stress hormone.  Perhaps a low carb diet is stressful on the body.  They also found higher levels of C-reactive protein or CRP which is a marker for inflammation and heart health risk.

Bottomline, it seems that the low carb diet produces faster weight loss results compared to low fat diets, helps increase metabolism and surprisingly does not increase cholesterol and triglyceride levels (it actually showed a significant decrease in these levels).  However, there is a small risk of ketoacidosis and some evidence that it may cause more stress and inflammation in the body.  

Many of these studies which show benefit are short term, usually less than a year, so we don’t know the long term effects of this diet yet.