Now that I've finally finished my article for the American Diabetes Association, I'd like to start by expressing my sincere appreciation for those who write scholarly articles and books. The time and effort it takes to produce accurate, substantive work is much more than many would expect. So to all the authors of my favorite nutrition books of 2011, thank you so much for the time you put in! My article was only a few pages long and took more hours than I care to admit. Fortunately, doing the research for it provided me with some good ideas for future blogs posts.
I was asked to write the article on a low-carbohydrate diet pattern for blood sugar and weight management in people with diabetes. The amount and type of carbohydrates to prescribe was at my own discretion, and I gave it very careful consideration after reviewing all of the available evidence. Although I've never personally cut carbs to the point necessary to induce ketosis, I was open to the possibility that there was evidence to warrant its use in diabetes and weight management. There has been a lot of research in this area within the past ten years, both short- and long-term studies, and I ended up citing 27 of them in the article.
Traditional ketogenic diets are extremely low in carbohydrates (usually 10-15 grams per day) and have been used since the 1920s for the treatment of childhood epilepsy with very impressive results. There is also emerging evidence regarding their use in therapy for certain types of cancer and neurological disorders such as ALS and Parkinson's disease. Ketosis occurs when the body shifts from using glucose to ketone bodies and fatty acids as its primary fuel. The level at which this occurs varies somewhat among different people, but it's generally less than 50 grams per day. The most famous low-carbohydrate ketogenic diet (LCKD) is the Atkins Diet created by cardiologist Dr. Robert Atkins in the early 1970s. It is mainly used for weight loss but occasionally for blood sugar control as well. The plan involves starting off at an "induction phase" of 20 grams of carbohydrates and adding back carbs until reaching a "maintenance" level which is also individualized. Dr. Richard Bernstein, who has lived with Type 1 diabetes for more than 60 years, recommends strictly limiting carbohydates with the goal of achieving normal blood sugar levels. By keeping carbs within 30-35 grams per day and 6-12 grams meal, smaller insulin dosages are needed, resulting in less error in matching carbohydrate intake to insulin and more predictable blood sugars. For people with Type 2 diabetes not taking insulin, very-low-carbohydrate intake prevents post-meal blood glucose spikes.
Is there any advantage to a VLCKD vs. a diet that is low in carbs but not low enough to promote ketosis? From the research I've seen, the answer is no with respect to the ketogenic aspect of the diet. The carbohydrate restriction itself is another matter, however. Do Dr. Bernstein and many other people with Type 1 and Type 2 diabetes experience better blood sugar control with carb intake at ketogenic levels? Definitely a very large portion do, but this is due to the diet's effect on blood sugar regulation. For these individuals, the benefits of VLCKDs may very well warrant its use. But for weight management, I just don't think that's the case. Millions of people have lost weight on Atkins or other low-carbohydrate plans, but many have never achieved their personal weight goals, and most have regained at least a portion of the weight back.
Although it doesn't work for everyone, I do believe a low-carbohydate diet can help people lose and maintain weight. Starting off at ketogenic levels may provide a psychological benefit due to early rapid weight loss that usually occurs, but there is certainly no indication to remain in perpetual ketosis for weight management purposes. While many low-carb proponents speak of a "metabolic advantage" that occurs with ketosis, characterized as turning your body into a fat-burning machine, I have found no convincing research to support this. It appears that the mechanism responsible for weight loss is a spontaneous reduction in calories due to reduced hunger and greater satiety on both low-carb diets and VLCKDs. And once a person reaches a certain weight, if the caloric intake is too high to promote further loss at this new weight, then weight loss will stall regardless of whether carb intake remains at ketogenic levels or not.
There may be another reason for slowed weight loss on a VLCKD. Recently, there have been several posts on various paleo/ancestral blogs regarding problems people have encountered on low-carb diets. I hadn't really been following this issue that closely since I was doing a lot of lit review for the article. But it seems the main issues people have encountered are failing to sustain continued weight loss despite keeping carbs low, an inability to stay warm, and fatigue. These are symptoms of potential thyroid dysfunction (among other things). There is a good amount of research indicating that people may develop problems converting the thyroid hormone thyroxine (T4) to the active hormone triiodothyronine (T3) and instead convert a greater than normal portion to the inactive form, reverse T3 (RT3) at lower carbohydrate intakes, with the effect being more pronounced at ketogenic levels. In certain individuals this may result in lower resting metabolic rate. It's important to note that this does not happen to everyone on VLCKDs, however, and thyroid function is very complex and affected by many factors in addition to carbohydrate and caloric intake.
I'm sure I'll probably lose several followers after this post, but I have to be honest and state my true beliefs as a dietitian and fellow low-carber. I've never advocated a ketogenic approach for weight management, and I received some very unpleasant e-mails and comments on another member's Facebook page when I recommended staying above 20 grams of carbs per day. (In that post, I neglected to mention the exceptions of treating epilepsy and possibly cancer and neurological disorders). As an outpatient dietitian in a large hospital, I counsel many people who are not even remotely interested in following a low carbohydrate diet, and that's fine. People can certainly lose weight and even control blood sugar (albeit with larger doses of medication) on a higher carb, lower fat diet. I'll be the first to admit that if I didn't have blood glucose issues I'd be eating more carbs.
I truly feel that people should listen to their bodies and eat in a way that works best for them. From a personal standpoint, I tried introducing safe starches to my diet for several weeks after reading about the brilliant Paul Jaminet's Perfect Health Diet and found that I could only tolerate just under 1/2 cup of potato or rice; any more and my blood sugar was well above 140 at the one-hour mark. To me such a small amount just isn't worth the prep time! So these days the majority of my carbs are coming from all kinds of fruit as well as yogurt. My total carb intake for the day is about 90-100 grams (65-75 grams digestible or net carbs), and this works well for me. I'd like you to do what works best for you. If you feel great on a VLCKD and are able to achieve and maintain your goal weight by following this plan, that's wonderful. But please be aware that ketosis isn't necessary to achieve weight loss. As with any diet, it is calories in vs. calories out that determines the ultimate outcome on the scale.
If you're wondering what my carbohydrate recommendations were for the article, as a general guideline I advised a starting point of about 85-110 grams of total carbohydrates (60-80 grams net carbs) per day using whole, unprocessed foods. (Interestingly, the Atkins website recommends 75+ net carbs daily, including grains, for lifetime maintenance). I know there will be many very-low-carb enthusiasts who think this is far too high, and I'm also expecting a backlash from other dietitians saying it's way too low, unsafe, unsustainable, lacking in nutrients, and, of course, too high in fat and protein. But I feel good about these recommendations given the research I've reviewed along with my own experience and that of others. You know the lyrics from that old song: You can't please everyone, so you better please yourself.
1. Zhou W, et al. The calorically restricted ketogenic diet, an effective alternative therapy for malignant brain cancer.
Nutr Metab 2007; 4:5
2. Zhong Z, et al. A ketogenic diet as a potential novel therapeutic intervention in amyotrophic lateral sclerosis.
BMC Neurosci 2006: 7:29
3. Johnson CS, et al.: Ketogenic low-carboydrate diets have no metabolic advantage over non-ketogenic low-carbohydate diets. Am J Clin Nutr 2006; 83:1055-1061
4. Martin CK, et al. Change in food cravings, food preferences, and appetite during a low-carbohydrate and low-fat diet. Obesity 2011; 19:1963-19704.
5. Bisschop PH, et al. Isocaloric carbohydrate deprivation induces protein catabolism despite a low T3-syndrome in healthy men. Clin Enocrinol 2001; 54:75-80
The term "low carb" is not easily defined. Low as compared to what? The Recommended Dietary Allowance (RDA) for minimum carbohydrate intake, as set by the Institute of Medicine's Food and Nutrition Board, is 130 grams per day. This is the level which dietitians are taught to instruct people never to go below "in order to maintain brain function." This recommendation is based on the central nervous system's daily requirement for about 130 grams of glucose (NOT carbohydrates). Further confusing the issue, the Reference Daily Intake (RDI) for carbohydrate (also set by the Food and Nutrition Board) "to meet the needs of 97-98% of healthy individuals" is 300 grams for a diet containing 2000 calories and 375 grams for a 2500- calorie diet (You can see find these numbers in the Daily Values section on any nutrition facts label). Why the disparity? Because the Board recommends that carbohydrates make up 45-65% of caloric intake. For someone eating 2000 calories daily, going with the average of 55% , this is 1100 calories or 275 grams of carbs. Not exactly 300 grams, but close. I'm not sure why the Board didn't set the value at 250 grams, or 45% of calories, since this would still be more than sufficient to meet people's needs and is nearly double the RDA. But for whatever reason, the RDI I is set at 300 grams.
So is low carb anything below 300 grams, then? Well, few people would argue that eating 280 grams of carbs a day constitutes a low-carbohydrate diet. Most would consider less than 150 grams to be low carb, or moderately low carb at the upper limit. Of course, there's a big difference between 15 grams of carbohydrates vs. 149 grams per day. Also, are we talking about total carbs or digestible ("net") carbs, calculated by subtracting the fiber from the total carb content? Some people count total carbs (starch, sugar, and fiber), some count only digestible carbs, and some follow the recommendation of the American Diabetes Association to subtract half the carbs from the total if the item in question has more than 5 grams of fiber. I prefer counting only digestible carbs, and I eat about 60 grams per day, which equates to 80-90 grams total carbs. More important for me is the amount of carbohydrates per sitting, because anything over 20-25 grams of digestible carbs usually results in higher blood sugar readings than I'm comfortable with.
Is there a carbohydrate level that is too low to be considered healthy? That depends on which studies you feel are reliable and, I would argue, your feelings about carbohydrate restriction. There also isn't a lot of research out there on low carbohydrate diets that provide enough calories; most were conducted on subjects consuming very-low-calorie diets, anywhere from 500-1000 calories per day. (There was also at least one that provided excessive calories, which opens up a whole other issue). Another problem is the short duration of some of the studies, since it typically takes time for the body to acclimate to lower carbohydrate intake. As long as there is sufficient protein and fat in the diet, gluconeogenesis will provide additional glucose to be used to fuel certain portions of the brain, the retinas, the red blood cells, and the kidneys, and ketone bodies produced from the metabolism of fat will supply energy for the cells and organs that don't require glucose (all of the others, including parts of the brain).
There is research suggesting that a minimum of 50 grams of carbohydrates per day is required to maintain proper conversion of the thyroid hormone T4 to the active form, T3, and to prevent excessive production of reverse T3. However, there is a fair amount of anecdotal evidence that some people can go well below 50 grams without developing this problem. Those who follow Atkins and other low-carb plans typically start on an induction phase of less than 20 grams daily for several weeks or months, gradually adding back carbs as they approach maintenance, and many appear to maintain normal thyroid function while eating very little carbohydrate.
Daily carbohydrate intake of 20 grams per day on a long-term basis may be too low for some people, although fine for others. I personally know a few people who comfortably subsist on this amount or less. Dr. Richard Bernstein is an example of a person with Type 1 diabetes who has strictly maintained a 30-gram-carb-per-day intake for over 40 years with no apparent ill effects nor any diabetes-related complications like retinopathy, neuropathy, nephropathy, or cardiovascular disease. He also appears fit and still maintains a busy practice at the age of 76. Obviously, this very-low-carbohydrate diet is definitely working well for him, as I know it has for many others.
So back to the original question: How low is too low? As with almost everything else, how one responds to carbohydrates is highly individualized. Some people will do well on 30 or fewer grams of carbs indefinitely, while others may feel best eating 100 grams or more, and most will fall somewhere in between. Optimal carbohydrate intake is fluid and may vary from day to day, month to month, and year to year. We need to take into consideration how we feel energy-wise as well as how various carbohydrate levels affect our weight, blood sugars, blood lipids, and thyroid hormones.
I don't think it's right to assign a minimum carbohydrate requirement of 130 grams for brain function -- some of the most brilliant doctors and scientists out there consume far less than this -- and I believe 300 grams is too high for the vast majority of adults, although I do have friends who regularly consume 300-400 grams daily and manage to stay in amazing shape with great energy and normal labs. I respect the right of every person to make the choice about what is right for himself or herself, and I would never try to "push" low-carbing on anyone who wasn't interested. However, I feel strongly that carbohydrate restriction should be presented as a healthy option, given its many benefits and the success that so many have had with it. While I'm fortunately not the only dietitian who feels this way, I'm definitely in the minority. I remain hopeful that the powers that be will accept carbohydrate restriction as a legitimate way of eating someday very soon!
1. Panel on the Dietary Reference Intakes for Macronutrients, Institute of Medicine. Dietary reference intakes for energy, carbohydrates, fiber, fat, fatty acids, cholesterol, protein, and amino acids. Washington, DC: National Academies Press, 2002.
2. Burman KD, et al: Glucose modulation of alterations in serum iodothyronine concentrations induced by fasting. Metabolism ,1979 Apr;28 (4): 291–299
3.Volek JS, et al. Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism, 2002 Jul; 51 (7): 864-870.
Franziska Spritzler, RD, CDE