Such diets are sometimes ketogenic (i.e. they restrict carbohydrate intake sufficiently to cause ketosis) for example, the induction phase of the Atkins diet. Some sources, though, consider less restrictive variants to be low-carbohydrate as well.
Apart from obesity, low-carbohydrate diets are often used as treatments for some other conditions, most notably diabetes and epilepsy, but also for chronic fatigue syndrome (see ketosis) and polycystic ovarian syndrome.,
Low-carbohydrate diet History,
Low-carbohydrate diet Beginnings,
Some anthropologists believe that early humans were hunter-gatherers consuming diets high in both protein and fat and mostly low in nutritive carbohydrates (although their diets would have been high in fiber). Indeed some isolated societies exist today which consume these types of diets. The advent of agriculture brought about the rise of civilization and the gradual rise of carbohydrate levels in human diets. The modern age has seen a particularly steep rise in refined carbohydrate levels in Western societies.
In 1863 William Banting, an obese English undertaker and coffin maker, published "Letter on Corpulence Addressed to the Public" in which he described a diet for weight control giving up bread, butter, milk, sugar, beer and potatoes. His booklet was widely read, so much so that some people used the term "Banting" for the activity usually called "dieting.".
In 1967, Dr. Irwin Stillman published The Doctor's Quick Weight Loss Diet. The "Stillman Diet" is a high-protein, low-carbohydrate and low-fat diet. It is regarded as one of the first low-carbohydrate diets to become popular in the US. Other low-carbohydrate diets in the 1960s included the Air Force Diet and the Drinking Man’s Diet. Austrian physician Dr Wolfgang Lutz published his book Leben Ohne Brot (Life Without Bread) in 196 However, it was hardly noticed in the English speaking world.
In 1972, Dr. Robert Atkins published Dr. Atkins Diet Revolution which advocated a low-carbohydrate diet he had successfully used in treating patients in the 1960s (having himself developed the diet from an unspecified article published in JAMA). The book met with some success but, because of research at that time suggesting risk factors associated with excess fat and protein, it was widely criticized by the mainstream medical community as being dangerous and misleading, thereby limiting its appeal at the time. Among other things critics pointed out that Dr. Atkins had done little real research into his theories and based them mostly on anecdotal evidence. Later that decade, Walter Voegtlin and Dr. Herman Tarnower published books advocating the Stone age diet and Scarsdale diet, respectively, each meeting with moderate success.
The concept of the glycemic index was developed about 1981 by Dr. David Jenkins to account for variances in speed of digestion of carbohydrates (e.g., the sugar in cooked carrots has more rapid effect than pure glucose). This concept classifies foods according to the rapidity of their effect on blood sugar levels – with fast digesting simple carbohydrates causing a sharper increase and slower digesting complex carbohydrates such as whole grains a slower one. The concept has been extended to include amount of carbohydrate actually absorbed as well, as a tablespoonful of cooked carrots is clearly less significant overall than a large baked potato (effectively pure starch, which is efficiently absorbed as glucose), despite differences in glycemic index.
Low-carb diets since the 1990s
In the 1990s Dr. Atkins published Dr. Atkins New Diet Revolution and other doctors began to publish books based on the same principles. This has been said to be the beginning of the "low carb craze." During the late 1990s and early 2000s low-carbohydrate diets became some of the most popular diets in the U.S. (by some accounts as much as 18% of the population was using a low-carbohydrate diet at its peak) and spread to many countries. These were noted by some food manufacturers and restaurant chains as substantially affecting their businesses (notably Krispy Kreme). Some in the mainstream medical community continued to denounce low-carbohydrate diets as being a dangerous trend.It is, however, valuable to note that many of these same doctors and institutions at the same time quietly began altering their own advice to be closer to the low-carbohydrate recommendations (e.g. eating more protein, eating more fiber/less starch, reducing consumption of juices by children). The low-carbohydrate advocates did some adjustments of their own increasingly advocating controlling fat and eliminating trans fat. Many of the diet guides and gurus that appeared at this time intentionally distanced themselves from Atkins and the term low carb (because of the controversies) even though their recommendations were based on largely the same principles (e.g. the Zone diet). As such it is often a matter of debate which diets are really low-carbohydrate and which are not. The 1990s and 2000s also saw the publication of an increased number of clinical studies regarding the effectiveness and safety (pro and con) of low-carbohydrate diets (see low-carbohydrate diet medical research).
After 2004 the popularity of this diet trend began to wane significantly although it still remains quite popular. In spite of the decline in popularity this diet trend has continued to quietly garner attention in the medical and nutritional science communities.,
Low-carbohydrate diet Practices and theories,
The term "low-carbohydrate diet" today is most strongly associated with the Atkins Diet. However, there is an array of other diets that share to varying degrees the same principles (e.g. the Zone Diet, the Protein Power Lifeplan,the Go Lower Diet,The Earth Diet and the South Beach Diet). Therefore, there is no widely accepted definition of what precisely constitutes a low-carbohydrate diet. It is important to note that the level of carbohydrate consumption defined as low-carbohydrate by medical researchers may be different from the level of carbohydrate defined by diet advisors. For the purposes of this discussion, this article focuses on diets that reduce (nutritive) carbohydrate intake sufficiently to dramatically reduce insulin production in the body and to encourage ketosis (production of ketones to be used as energy in place of glucose).
Although originally low-carbohydrate diets were created based on anecdotal evidence of their effectiveness, today there is a much greater theoretical basis on which these diets rest. The key scientific principle which forms the basis for these diets is the relationship between consumption of carbohydrates and the subsequent effect on blood sugar (i.e. blood glucose) and on production of some hormones. Blood sugar levels in the human body must be maintained in a fairly narrow range to maintain health. The two primary hormones related to regulating blood sugar levels, produced in the pancreas, are insulin, which lowers blood sugar levels (among many other effects, most of considerable significance metabolically), and glucagon, which raises blood sugar levels. In general, most western diets (and many others) are sufficiently high in nutritive carbohydrates that nearly all meals evoke insulin secretion from the beta cells in the pancreas; carbohydrates which are digested to produce glucose in the blood stream are the primary control for insulin secretion. Another aspect of insulin secretion is control of ketosis; in the non-ketotic state, the human body stores dietary fat in fat cells (i.e., adipose tissue) and preferentially uses glucose as cellular fuel. By contrast, low-carbohydrate diets, or more properly, diets that are very low in nutritive carbohydrates, evoke less insulin (to cover the ingested glucose in the blood stream), leading to longer and more frequent episodes of ketosis. Some researchers suggest that this causes body fat to be eliminated from the body, although this theory remains, at best, controversial, if it refers to excretion of lipids (i.e., fat and oil) and not to fat metabolism during ketosis.
Low-carbohydrate diet advocates in general recommend reducing nutritive carbohydrates (commonly referred to as "net carbs," i.e. grams of total carbohydrates reduced by the non-nutritive carbohydrates) to very low levels. This means sharply reducing consumption of desserts, breads, pastas, potatoes, rice, and other sweet or starchy foods. Some recommend levels as low as 20-30 grams of "net carbs" per day, at least in the early stages of dieting (for comparison, a single slice of white bread typically contains 15 grams of carbohydrate, almost entirely starch). By contrast, the U.S. Institute of Medicine recommends a minimum intake of 130 grams of carbohydrate per day (the FAO and WHO similarly recommend that the majority of dietary energy come from carbohydrates).
Low-carbohydrate diets often differ in the specific amount of carbohydrates allowed, whether certain types of foods are preferred, whether occasional exceptions are allowed, etc. Generally they all agree that processed sugar should be eliminated, or at the very least greatly reduced, and similarly generally discourage heavily processed grains (white bread, etc.). They vary greatly in their recommendations as to the amount of fat allowed in the diet although the most popular versions today (including Atkins) generally recommend at most a moderate fat intake. The American Academy of Family Physicians defines low-carbohydrate diets as diets that restrict carbohydrate intake to 20g to 60g per day. Atkins (in the later phases) and some other low-carbohydrate diets exceed the 60g limit definition by this group.
Although low-carbohydrate diets are most commonly discussed as a weight-loss approach, some experts have proposed using low-carbohydrate diets to mitigate or prevent diseases ranging from diabetes to epilepsy. Indeed, it has been argued by some low-carbohydrate proponents and others that it is the rise in carbohydrate consumption, especially refined carbohydrates, that has caused the epidemic levels of many diseases in modern society.
There is also a category of diets known as low-glycemic-index diets (low-GI diets) or low-glycemic-load diets (low-GL diets), in particular the Low GI Diet by Brand-Miller et al. In reality, low-carbohydrate diets can also be low-GL diets (and vice versa) depending on the carbohydrates in a particular diet. In practice, though, "low-GI"/"low-GL" diets differ from "low-carb" diets in the following ways. First, low-carbohydrate diets treat all nutritive carbohydrates as having the same effect on metabolism, and generally assume that their effect is predictable. Low-GI/low-GL diets are based on the measured change in blood glucose levels in various carbohydrates - these vary markedly in laboratory studies. The differences are due to poorly understood digestive differences between foods. However, as foods influence digestion in complex ways (e.g., both protein and fat delay absorption of glucose from carbohydrates eaten at the same time) it is difficult to even approximate the glycemic effect (e.g., over time or even in total in some cases) of a particular meal.
Another related diet type, the low-insulin-index diet, is similar except that it is based on measurements of direct insulemic responses (i.e., the amount of insulin in the bloodstream) to food rather than glycemic response (the amount of glucose in the bloodstream). Although such diet recommendations mostly involve lowering nutritive carbohydrates, there are some low-carbohydrate foods that are discouraged as well (e.g., beef). Insulin secretion is stimulated (though less strongly) by other dietary intake. Like glycemic index diets, there is difficulty predicting the insulin secretion from any particular meal, due to assorted digestive interactions and so differing effects on insulin release.
Ketosis and insulin synthesis: what is normal?
At the heart of the debate about most low carbohydrate diets are fundamental questions about what is a normal diet and how the human body is supposed to operate. These questions can be outlined as follows:
The diets of most people in modern western nations, especially the United States, contain large amounts of starches and often substantial amounts of sugars, including fructose. Most westerners seldom exhaust stored glycogen supplies and hence rarely go into ketosis. This has been regarded by medical science in the last century as normal for humans.[citation needed] Ketosis had widely been regarded as harmful and potentially life-threatening, unnecessarily stressing the liver and causing destruction of muscle tissues,[citation needed] and ketosis had sometimes been confused with ketoacidosis, a dangerous and extreme ketotic condition associated with diabetes. A perception developed that getting energy chiefly from dietary protein rather than carbohydrates causes liver damage and that getting energy chiefly from dietary fats rather than carbohydrates causes heart disease and other health problems. This view is still held by the majority of those in the medical and nutritional science communities. However, it is now widely recognized that periodic ketosis is in fact normal, and that ketosis provides a number of surprising benefits, including neuroprotection against diverse types of cellular injury.
People who eschew low carbohydrate diets cite hypoglycemia and ketoacidosis as a risk factor, but these are only problematic for people such as diabetics, who have impaired regulation of gluconeogenesis and ketone metabolism.
A diet very low in starches and sugars induces several adaptive responses. Low blood glucose causes the pancreas to produce glucagon, which stimulates the liver to convert stored glycogen into glucose and release it into the blood. When liver glycogen stores are exhausted, the body starts utilizing fatty acids instead of glucose. The brain cannot use fatty acids for energy, and instead uses ketones produced from fatty acids by the liver. By using fatty acids and ketones as energy sources, supplemented by conversion of proteins to glucose (gluconeogenesis), the body can maintain normal levels of blood glucose without dietary carbohydrates.
Most advocates of low-carbohydrate diets, such as the Atkins Diet, argue that the human body is adapted to function primarily in ketosis. They argue that high insulin levels can cause many health problems, most significantly fat storage and weight gain. They argue that the purported dangers of ketosis are unsubstantiated (some of the arguments against ketosis result from confusion between ketosis and ketoacidosis which is a related and very dangerous condition). They also argue that fat in the diet only contributes to heart disease in the presence of high insulin levels and that if the diet is instead adjusted to induce ketosis, fat and cholesterol in the diet are not a major concern (although most do not advocate unrestricted fat intake and do advocate avoiding trans fat).
On a high-carbohydrate diet, glucose is used by cells in the body for the energy needed for their basic functions, and about 2/3 of body cells require insulin in order to use glucose. Excessive amounts of blood glucose are thought to be a primary cause of the complications of diabetes; when glucose reacts with body proteins (resulting in glycosolated proteins) and change their behavior. Perhaps for this reason, the amount of glucose tightly maintained in the blood is quite low. Unless a meal is very low in starches and sugars, blood glucose will rise for a period of an hour or two after a meal. When this occurs, beta cells in the pancreas release insulin to cause uptake of glucose into cells. In liver and muscle cells, more glucose is taken in than is needed and stored as glycogen (once called 'animal starch'), Diets with a high starch/sugar content, therefore, cause release of more insulin and so more cell absorption. In diabetics, glucose levels vary in time with meals and vary a little more as a result of high carbohydrate content meals. In non-diabetics, blood sugar levels are restored to normal levels within an hour or two, regardless of the content of a meal.
It is worth noting that while there are Essential Fatty Acids(EFA) and Essential Amino Acids(EAA) there are no essential carbohydrates of any sort and while a diet devoid of EFA or EAA will result in eventual death, a diet completely without carbohydrates can be maintained indefinitely without health detriment.
Scientific research
Because of the substantial controversy regarding low-carbohydrate diets and even disagreements in interpreting the results of specific studies, it is difficult to objectively summarize the research in a way that reflects scientific consensus. Although there has been some research done throughout the twentieth century, most directly relevant scientific studies have occurred in the 1990s and early 2000s and, as such, are relatively new. Researchers and other experts have published articles and studies that run the gamut from promoting the safety and efficacy of these diets to questioning their long-term validity to outright condemning them as dangerous. Until recently a significant criticism of the diet trend was that there were no studies that evaluated the effects of the diets beyond a few months. However, studies are emerging which evaluate these diets over much longer periods, controlled studies as long as two years and survey studies as long as two decades.
A meta-analysis of randomized controlled trials by the Cochrane Collaboration in 2002 concluded that fat-restricted diets are no better than calorie restricted diets in achieving long term weight loss in overweight or obese people. A 2003 meta-analysis that included a randomized controlled trials published after the Cochrane review found that "low-carbohydrate, non-energy-restricted diets appear to be at least as effective as low-fat, energy-restricted diets in inducing weight loss for up to 1 year. A 2007 JAMA study comparing the effectiveness of the Atkins low-carb diet to several other popular diets concluded "In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets."
Potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol values when low-carbohydrate diets to induce weight loss are considered. A 2008 systematic review of randomized controlled studies that compared low-carbohydrate diets to low-fat/low-calorie diets and found that measurements of weight, HDL cholesterol, triglyceride levels and systolic blood pressure were significantly better in groups that followed low-carbohydrate diets. The authors of this review also found a higher rate of attrition in groups with low-fat diets, and concluded that "evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year," but they also called for more long-term studies.
In addition to research on the efficacy of the diets some research has directly addressed other areas of health affected by low-carbohydrate diets. Contrary to popular belief that low-carbohydrate diets damage the heart, a couple of studies confirmed that people eating low-carbohydrate, high-fat/protein diets had the same or slightly less risk of coronary heart disease. Other studies have found possible benefits to individuals with diabetes, cancer,and autism. The ketogenic diet, with 80% of energy from fat and much of the remaining from protein, has been used since the 1920s to treat epilepsy. Modern effective anticonvulsant drugs mean that it is now used only for children with difficult-to-control epilepsy, and there may be cause for concern over issues such as stunted growth for these children.
A July 2009 study of existing dietary habits associated a low carbohydrate diet with obesity, although the study drew no explicit conclusion regarding the cause: Whether the diet resulted in the obesity or the obesity motivated people to adopt the diet.
Major governmental and medical organizations
Although opinions regarding low-carbohydrate diets vary greatly throughout the medical and nutritional science communities, major government bodies as well as major medical and nutritional associations have generally opposed this nutritional regimen. In recent years, however, some of these same organizations have gradually begun to relax their opposition to the point that some have even voiced cautious support for low-carbohydrate diets. The following are official statements from some of these organizations.
American Academy of Family Physicians
The AAFP released a discussion paper on the Atkins Diet specifically in 2006. Although the paper expresses reservations about the Atkins plan they acknowledge it as a legitimate weight loss approach.
American Diabetes Association
The ADA revised their Nutrition Recommendations and Interventions for Diabetes in 2008 to acknowledge low-carbohydrate diets as a legitimate weight-loss plan. The recommendations fall short of endorsing low-carbohydrate diets as a long-term health plan nor do they given any preference to these diets. Nevertheless, this is perhaps the first statement of support—albeit for the short-term—by one of the foremost medical organizations. In its 2009 publication of Clinical Practice Recommendations, The ADA again reaffirmed its acceptance of carbohydrate-controlled diets as an effective treatment for short-term (up to one year) weight loss among obese people suffering from type two diabetes.
American Dietetic Association
As of 2003 in commenting on a study in the Journal of the American Medical Association, a spokesperson for the American Dietetic Association reiterated the association's belief that "there is no magic bullet to safe and healthful weight loss." The Association specifically endorses the high-carbohydrate diet recommended by the National Academy of Sciences.
American Heart Association
The official statement from the AHA regarding these diets states categorically that the association "doesn't recommend high-protein diets." A science advisory from the association further states the associations belief that these diets are "associated with increased risk for coronary heart disease." The AHA has been one of the most adamant opponents of low-carbohydrate diets. Dr. Robert Eckel, past president, noted that the association supported low-fat and low-saturated-fat diets, but that a low-carbohydrate diet could potentially meet AHA guidelines.
Australian Heart Foundation
The position statement by the Heart Foundation regarding low-carbohydrate diets states that "the Heart Foundation does not support the adoption of VLCARB diets for weight loss." Although the statement clearly recommends against use of low-carbohydrate diets it makes clear that their major concern is saturated fats as opposed to carbohydrate restriction and protein. Moreover, other statements suggest that their position might be re-evaluated in the event of more evidence from longer-term studies.
Food Standards Agency (UK)
The consumer advice statements of the FSA regarding low-carbohydrate diets state that "rather than avoiding starchy foods, it's better to try and base your meals on them." They further state concerns regarding fat consumption in low-carbohydrate diets.
Heart & Stroke Foundation (Canada)
The official position statement of the Heart & Stroke Foundation states "Do not follow a low carbohydrate diet for purposes of weight loss." They state concerns regarding numerous health risks particularly those related to high consumption of "saturated and trans fats".
National Board of Health and Welfare (Sweden)
In 2008, the Socialstyrelsen in Sweden altered its standing regarding low-carbohydrate diets. Although formal endorsement of this regimen has not yet appeared, the government has given its formal approval for using carbohydrate-controlled diets for medically supervised weight loss.
U.S. Department of Health and Human Services
The HHS issues consumer guidelines for maintaining heart health which state regarding low-carbohydrate diets that "they're not the route to healthy, long-term weight management." Nevertheless HHS has issued some statements indicating wavering on this position.
Criticism and controversies
Water-related weight loss
In the first week or two of a low-carbohydrate diet a great deal of the weight loss comes from eliminating water retained in the body (many doctors say that the presence of high levels of insulin in the blood causes unnecessary water retention in the body). However, this is a short-term effect and is entirely separate from the general weight loss that these diets can produce through eliminating excess body fat.,
Low-carbohydrate diet Exercise,
Some critics argue that low-carbohydrate diets can inherently cause weakness or fatigue giving rise to the occasional assumption that low-carbohydrate dieting cannot involve an exercise regimen. Advocates of low-carbohydrate diets generally dispute any suggestion that such diets cause weakness or exhaustion (except in the first several days as the body adjusts) and indeed most highly recommend exercise as part of a healthy lifestyle. There is a large body of evidence stretching back to the 1880s that shows that physical performance is not negatively affected by ketogenic diets once a person has been acclimatized to such a diet. Arctic cultures such as the Inuit and African cultures such as the Masai Tribesmen lead physically demanding lives in some of the harshest climates on Earth and yet consume a diet almost completely devoid of carbohydrate.,
Vegetables and fruits,
Many critics argue that low-carbohydrate diets inherently require minimizing vegetable and fruit consumption which in turn robs the body of important nutrients. Some critics imply or explicitly argue that vegetables and fruits are inherently all heavily concentrated sources of carbohydrates (so much so that some sources literally treat the words vegetable and carbohydrate as synonymous). While some fruits may contain relatively high concentrations of sugar, most fruit is largely water and not particularly calorie-dense. Thus, in absolute terms, even sweet fruits and berries do not represent a significant source of carbohydrates in their natural form and also typically contain a good deal of fiber which attenuates the absorption of sugar in the gut and lastly, most of the sugar in fruit is fructose which, in obese subjects, has a reported negligible effect on insulin levels. Most vegetables are low- or moderate-carbohydrate foods (note that in the context of these diets fiber is excluded because it is not a nutritive carbohydrate). Some vegetables like Potatoes, rice, maize (corn), and others, have high concentrations of starch. Most low-carbohydrate diet plans accommodate vegetables such as broccoli, spinach, cauliflower, and peppers. Nevertheless debate remains as to whether restricting even just high-carbohydrate fruits, vegetables, and grains is truly healthy.
Contrary to the recommendations of most low-carbohydrate diet guides, some individuals may choose to avoid vegetables altogether in order to minimize carbohydrates. Low-carbohydrate vegetarianism is also practiced.Carrot sticks and veggie sticks are especially useful in low carb diet recipes.,
Micronutrients and vitamins,
The major low-carbohydrate diet guides generally recommend multi-vitamin and mineral supplements as part of the diet regimen which may lead some to believe that these diets are nutritionally deficient. The primary reason for this recommendation is that if the switch from a high-carbohydrate to a low-carbohydrate, ketogenic diet is rapid, the body can temporarily go through a period of adjustment during which the body may require extra vitamins and minerals (the reasons have to do with the body's releasing excess fluids that were stored during high-carbohydrate eating). In other words, the body goes through a temporary "shock" if the diet is changed to low-carbohydrate dieting quickly just as it would changing to a high-carbohydrate diet quickly. This does not, in and of itself, indicate that either type of diet is nutritionally deficient. While it is true that many foods that are rich in carbohydrates are also rich in vitamins and minerals, there are many low-carbohydrate foods that are similarly rich in vitamins and minerals.,
Low-carbohydrate diet Glucose availability,
A common argument in favor of high-carbohydrate diets is that most carbohydrates break down readily into glucose in the bloodstream and, therefore, the body does not have to work as hard to get its energy in a high-carbohydrate diet as a low-carbohydrate diet. This argument, by itself, is incomplete. Although many dietary carbohydrates do break down into glucose, most of that glucose does not remain in the bloodstream for long. Its presence stimulates the beta cells in the pancreas to release insulin which has the effect of causing about 2/3 of body cells to take in glucose, and to cause fat cells to take in fatty acids and store them. As the blood glucose level falls, the amount of insulin released is reduced; the entire process is completed in non-diabetics in an hour or two after eating.High-carbohydrate diets require more insulin production and release than low-carbohydrate diets and there is some evidence that the increasingly large percentage of calories consumed as carbohydrates has led to the increased incidence of metabolic disorders such as Type 2 Diabetes
In addition, this claim neglects the nature of the carbohydrate ingested. Some are indigestible in humans (e.g., cellulose), some are poorly digested in humans (e.g., the amylose starch variant), and some requires considerable processing to be converted to absorbable forms, In general, uncooked or unprocessed (e.g., milling, crushing, etc.) foods are harder (typically much harder to absorb and so do not raise glucose levels as much as might be expected from the proportion of carbohydrate present. Cooking (especially moist cooking above the temperature necessary to expand starch granules), and mechanical processing, both considerably raise the amount of absorbable carbohydrate and reduce the digestive effort required. Analyses which neglect these factors are misleading and will not result in a working diet, or at least one which works as intended. (See Catching Fire, Richard Wrangham)
In fact, there is some evidence that the human brain, the largest consumer of glucose in the body can operate more efficiently on ketones.
Other controversies
In 2004, the Canadian government ruled that foods sold in Canada could not be marketed with reduced or eliminated carbohydrate content as a selling point because reduced carbohydrate content was not determined to be a health benefit, and that existing "low carb" and "no carb" packaging would have to be phased out by 2006.
Some variants of low carbohydrate diets involve substantially lowered intake of dietary fiber which can result in constipation if not supplemented. For example, this has been a criticism of the Induction stage of the Atkins diet (note that today the Atkins diet is more clear about recommending a fiber supplement during Induction). Most advocates today argue that fiber is a "good" carbohydrate and in fact encourage a high-fiber diet.
It has been hypothesized that a diet-related change in blood acidity can lead to bone loss through a process called ketoacidosis, as mentioned earlier in this article. However ketoacidosis, which is often confused with ketosis, is an acute medical condition caused by extreme fasting or as a symptom of untreated diabetes, and is not likely to be induced by an otherwise adequate low-carbohydrate diet.
One of the occasional side effects of a ketogenic diet is a noticeable smell of ketones in the urine, perspiration, and breath. This is caused by the presence of larger than usual amounts of the three ketone bodies normally produced during fat metabolism. One of the ketone bodies is actually a ketone, acetone, and it is released via the lungs. It has a characteristic smell, often said to resemble fruit or nail polish remover. In most cases, periodic ketosis (as occurs between widely separated meals) does not cause a noticeable odor. When the other two ketone bodies are produced in large quantities, the resulting condition is called ketoacidosis, and can be quite dangerous as even small changes in blood pH are incompatible with life.
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