Low carbohydrate diet

By Nebil Abdillahi

Low carbohydrate diets are some of the most popular diets in America, which is generating multi-billion dollar businesses.  Many of the people who pursue this type of diet don’t stop to question whether or not a low carbohydrate diet is really the healthiest way to lose weight.  It seems as though the most important concept to people in society is not staying healthy but staying thin by any means necessary. Society has planted the misconception in peoples minds that the only way to be accepted as “beautiful” is to look extremely thin.
This misconception that many people have adopted in society about weight has caused many people to spend large amounts of money on products that are not exactly healthy such as New Diet Revolution, Sugar Busters, Protein Power, The Zone, and The Carbohydrate Addict’s Diet. However, they all recommend a very strict reduction in the consumption of carbohydrates. All of these books promise consumers that one can achieve a ideal body by eating steak, fatty sausage, bacon, fried chicken, or cheese products, as long as they stay way from rice, bread and potatoes. In addition to achieving an ideal body, the diet promises other health benefits such as low blood sugar and cholesterol. Despite the popularity of this type of diet, there is compelling evidence against low-carbohydrate and high protein diets.

What is a low carbohydrate, high protein diet?
Promoters of low carbohydrate diets tell people that people that they will lose weight and will be able to keep the weight off. The diet usually consists of severely limiting the intake of sugar, rice, pasta, cereal, bread, and fruit. However, people are allowed to eat unlimited animal products, such as meat, poultry, eggs, butter, and cream. A typical low carbohydrate diet of at least 60 to 70 percent of daily calories intake comes from fat and carbohydrates that make up less than 10 percent in some cases, and less than 5 percent of daily calorie intake per day.  This situation is similar to the body’s process during prolonged fasting.
Promoters of this diet state that hyper insulin and insulin resistance, a common characteristic of obesity, will lower their insulin levels. Lowering insulin levels will help the body avoid storing fat. Insulin is the hormone that allows blood sugar to be used by the cells. In other words, by restricting carbohydrate intake, our main energy source glucose is eliminated. Therefore the body burns fat instead of glucose as energy thus promoting weight loss. The implication is that the dietary fat is not necessarily converted into body fat.  Carbohydrates, on the other hand, are readily converted into fat by the action insulin. When a person eats a high-carbohydrate meal, the increased blood sugar stimulates insulin production by the pancreas.
Insulin is the hormone that allows blood sugar to be used by the cells. However, a side effect of insulin is that it also causes fat to be deposited, which stimulates the brain to produce hunger signals that lead to consumption of more carbohydrates. As a result, the body cells become resistant to insulin, meaning that the pancreas has to work overtime to produce more insulin to keep up with the demand. Therefore, restricting intake of carbohydrates puts a stop to the progress of insulin.
 
Carbohydrate’s function in the diet for general health:
The primary function of carbohydrates is to provide energy for the body, especially the brain and the nervous system.  They also assist in the digestion and assimilation of food. In addition, carbohydrates provide a protein sparing effect. It does not matter how good the protein is because it will not be used efficiently without enough carbohydrates.  Carbohydrates also help to regulate protein and fat metabolism. 
When carbohydrate reserves are reduced, the body will convert protein into glucose for energy. This can lead to gluconeogenesis, which causes the metabolic rate to slow down. When a person is on a carbohydrate free diet, protein is used as energy source. However, the excessive breakdown of proteins to sugars can lead to excessive ketones being formed in the liver.  In strict studies these people exhibited the same symptoms as those on a starvation regimen. Symptoms include abnormal fat metabolism, breakdown of body protein, increased sodium excretion, loss of energy and fatigue.
It has been found that a small amount of carbohydrates, between 50 to 100 g, can prevent these symptoms. The National Research Council, the Food and Agriculture Organization of the United Nations, and World Health Organization recommended that adults consume at least 55% of daily carbohydrates from a variety of sources. For example, a person with a 2,000 kcal diet represents 275 grams of that in carbohydrates. In addition, The United State Department of Agriculture recommends choosing carbohydrate-rich food from whole grains, rice, pasta, potatoes, fruits, and vegetables. To meet those recommendations, USDA suggests eating 6 to11 servings from bread, cereal, and grain group, 2 to 4 servings from the fruit group and 3 to 5 servings from the vegetable group each day.
Earlier it was stated that it does not matter how good proteins are because it will not be used efficiently without enough carbohydrates. These proteins can have an adverse affect on your bones. According to a study conducted by Barzel, Massey (1998) et al, dietary protein can have a negative effect on acid base metabolism and ultimately on urinary calcium and bone.
 
Evidence from the Research
What do people really think?
In today’s society many people believe that that there is only one strategy that can be done to promote weight loss, which is a low carbohydrate diet. A study was conducted by Smith, Burns, (2002) et al., to compare dietary fat-related behavior among adults who are trying to lose weight, avoid gaining weight, or are doing nothing in particular to control their weight and compare their beliefs about dietary fat related behavior. This study was done on 2,500 randomly selected adults.
Women who were trying to avoid weight gain believed that they should make a greater change in their dietary fat related behavior than did women who were trying to lose weight. The results of the study also suggest that men make fewer fat related changes when attempting to control weight and hence gender disparities in weight preoccupation may extend into weight-control practice. Also the results indicate that women attempting weight control are generally aware of the kinds of foods that should be limited in a weight control diet but it is of some concern that these foods tended to be completely avoided. 
Based on these results it is evident that women in particular who are trying to lose weight are not following a more conventional low fat diet but are probably engaging in “extreme or popular” diets such as low carbohydrate diets.
 
Low Carbohydrate Diets, Do They Really Work?
      Lean, Han (1997) examined anthropometric changes and cardiovascular benefits with high and low carbohydrate on a free living woman[1]. For this study, 110 free-living women in the age group between 18-68 years old were chosen with BMI between 25-50 kg/m2. The subjects received 1200 kcal diet of 58% or 35% carbohydrate (COH) for 12 weeks. The subject body weight, HDL and LDL cholesterol, triglyceride and blood pressure were measured. After three months, the study found out women on high CHO lost on average 4.3kg and those on low CHO lost 5.6kg of body weight.
Changes in risk factors did not significantly differ between the diet treatments throughout the study. However those on high CHO diets significantly lowered their plasma total cholesterol by 0.33 mmol, LDL cholesterol by 0.23 mmol and HDL cholesterol by 0.05 mmol, while women on low CHO diets lowered only plasma triglyceride by 0.28 mmol. Blood pressure did not change significantly on either diet.
After six months, women on high CHO lost 6.8kg and those on low CHO lost 6.8kg. On the high CHO diet, total cholesterol remained significantly below the baseline value at 0.34 mmol, triglyceride was significantly lowered by 0.27 mmol, and HDL returned to the baseline value. The study results provide some support for preferring a high CHO diet to lower CHO approach in weight management from the point of view of risk reduction.
However it also shows that a low carbohydrate diet can indeed lead to significant weight loss and body fat. 
More recently, Westman, Yancy et al (2002), also examine the effect of a low carbohydrate diet over a 6-month period. The study was conducted with fifty-one overweight or obese healthy volunteers who wanted to lose weight. The subjects were given a low carbohydrate diet consisting of less than 25g of carbohydrates per day for six months with no limit caloric intake as well as unlimited amount of meat and eggs. In addition the subject received nutritional supplementation, recommendations about exercise, and attended group meetings at a research clinic.
The method of measurement used was anthropometry, serum chemistry and lipid values, 24-hour urine measurements, and subjective adverse effects. At end of study the researchers found that 80% percent of the 51 subjects enrolled adhered to the diet program showed that their body weight decreased 10.3%, and had a BMI reduction of 3.2kg/m(2)). The mean percentage of fat reduced body weight was 2.9% from baseline to 6 months. Also the mean serum bicarbonate level decreased 2 mmol and blood urea nitrogen level increased 2mg/dl. Serum total cholesterol level decreased 11mg/dl , triglyceride level decreased 56mg/dl, high-density lipoprotein (HDL) cholesterol level increased 10mg/dl, and the cholesterol/HDL cholesterol ratio decreased 0.9units.
It is clear from the results that a low carbohydrate diet does lead to significant weight loss. However, there are certain limitations and applications of these studies due to the uncontrolled design, self report of several variables, and the use of skin fold calipers to estimate fat mass. Also because only healthy volunteers were studied, generalizing these results to include patients with medical illness is difficult.
 
Low Carbohydrate vs. High Carbohydrate Diets
According to Golay, Allaz, (1995) et al, a study was done to evaluate the effect of diets that were equally low in energy but widely different in relative amounts of fat and carbohydrate on body weight during a six week period of hospitalization.  The study involved 43 adults. The obese patients were studied before and after a 6-week period of hospitalization.  Subjects were randomly assigned to receive diets composed of either 32% protein 15% carbohydrate and 53% fat, or, 29% protein 45% carbohydrate and 26% fat. Skin folding and waist-to hip circumference tests were used to measure the body composition.
The study showed at the end of 6-week period that there was no significant difference in the amount of weight loss in response to diets containing either 15% or 53 % carbohydrate. Furthermore, significant decreases in total body fat, and waist to hip circumference changes were seen in both groups. Also, the study pointed out that the patients who received low energy diets that contained 15% carbohydrate showed a decrease in their fasting plasma glucose, insulin, cholesterol, and triacylglycerol concentrations; however, neither plasma insulin nor triacylglycerol concentrations decreased significantly in response to the higher carbohydrate diet. These findings suggest that it was energy intake that influenced the weight loss energy, not changes in macronutrient balance that promoted weight loss. In other words, the level of energy intake has the greatest impact on short-term fat reduction and changes in the diet composition affect fat reduction by ultimately affecting energy intake.
A similar study conducted by Golay, Eigenheer (1996) et al, tested to see the effects of two low calorie diets of similar caloric value, but differing in carbohydrate content. Sixty-eight outpatients were randomly put on low Carbohydrate diets. The study showed in both patients that the mean weight loss was similar and did not differ significantly between the two groups. Furthermore, loss of adipose tissue was similar among the subjects. In addition, waist/hip ratio was significantly reduced in both groups with identical results.  Also, fasting blood glucose along with cholesterol and triglyceride concentration was significantly decreased after weight loss. The glucose/insulin ratio improved significantly after weight loss with both diets. The study also showed that with high protein intake, the body composition changed.
The results of this study support the findings of Golay, Allaz (1995). It shows that neither diet offered a significant advantage in weight loss reduction when comparing weight loss or other metabolic parameters over a 12 week period. However, the results are more significant and general than Golay, Allaz (1995) due to a larger sample population.
Both studies however have shortcomings.  They are both brief, use a small population, and may be insufficient for significant results. In addition, we do not know whether the subject’s weight loss is permanent or much about any long-term side effect that may result from high intake of fat. Also, anthropometry is less accurate with human error values. A period, covering at least 24 weeks would provide the researchers with a longer observation period and therefore increase the ability to make a conclusion about the differences in the two diets.
Another study conducted by the USDA from 1994-1996, looked at the body weight of people eating low-carbohydrate, vegetarian, and other diets. The diets were rated according to the Healthy Eating Index (HEI) and the average BMI was calculated for different diet groups.
The results showed that the vegetarian group had a higher carbohydrate intake but a lower calorie intake and a lower BMI. They also had a lower HEI but not by much when compared to the non-vegetarian group. The non-vegetarian group was further subdivided into 3 categories (low, medium and high) based on carbohydrate intake. The most striking result from this was that persons in the highest carbohydrate intake category had the lowest calorie intake and did not weigh as much.
Overall this study indicates that low fat, high carbohydrate individuals had lower energy intake compared to the low carbohydrate individuals. This supports the results of Golay, Allaz (1995) and Golay, Eigenheer et al (year).
 
Conclusion
During the 1980’s and 1990’s, low fat diets were promoted where low fat foods were replaced by carbohydrates. People continued to get fatter however. The evidence presented here helps to reconcile this trend and also addresses the effectiveness of the now popular “low carbohydrate diet” which replaced the low fat diet.
The results indicate that even though low carbohydrate diets are effective at weight loss at least in the short term, they are not less effective than high carbohydrate diets. We are also unclear about the long term effects of low carbohydrate, high fat diets on the health of individuals since many of the studies did not conduct long periods of observation. This leads us to conclude that weight loss is independent of the carbohydrate, fat and protein components of the diet. The key to weight loss may lie in energy restriction and people are more likely to reduce their energy intake by reducing fat intake rather than by reducing carbohydrate intake.
 
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This article is for information purposes only. It is not meant to diagnose, treat or prevent any disease or condition. Consult your primary health care provider if you have or suspect you have any physical ailments

References
 
Barzel, U. S. Excess dietary protein can adversely affect bone. The Journal of Nutrition .1998;    128:1051-54.
Lean, M. Han, TS. Prvan, T. Richmond, PR. Avenell, A. Weight loss with high and low carbohydrate 1200 kcal diets in free living women. European Journal of Clinical Nutrition. 1997;51:243-248.
Westman, C.E. Yancy, W.S. et al. Effect of 6-Month Adherence to a Very Low Carbohydrate Diet Program. American Journal Medicine. 2002;113:30-6.
Goalay, F. Allaz, A. Morel, Y. et al. Similar weigh loss with low- or high-carbohydrate diets. The American Journal of Clinical Nutrition. 1996;63:174-77. 
Golay, C. Eigenheer, Y. el al. Weight loss with low or high carbohydrate diet? International Journal of Obesity. 1996;20:1067-1072.
Keenned, E.T. Bowman, S.A. Spence, J.T. et al. Popular diets: Correlation to health, nutrition, and obesity. Journal of the American Dietetic Association. 2001;101:411-420.
Mill, J. Holt, S. Pawlak, D. et al. What are the long range health implications of low carbohydrate, high protein, high fat diets. Journal of Clinical Nutrition. 2002; 76:281S-284S.
Timperio, A. Crawford, D. Burns, C. Behavior and belief related to dietary fat are influenced by weight control status. Journal of the American Dietetic Association. 2002; 102:88-91.
Lukaski HC. Methods for the assessment of human body composition: traditional and new. American Journal Clinical Nutrition. 1987;46:537-556.
  Fleming, R. The effect of high protein on Coronary Blood Flow. The Journal of Vascular Disease. 2000;51:817-826.
11. Gardzina, Y. Cotugna, N. Vickery, C. Should You recommend a low carb, high protein diet? The Nurse Practitioner. 2002;27:52-59
 
 
[1] Free Living Women are women who do not suffer from any disease, are not overweight and have not problems with calorie intake