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Carbohydrates: How Low is Too Low?

9/25/2011

28 Comments

 
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!

References:
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.

28 Comments
Mark link
9/26/2011 04:35:52 am

These figures are in stark contrast to the research that Taubes cites in Why We Get Fat. According that book, there is simply no minimum number of carb grams. The body produces what is needed for proper brain function.

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Franziska
9/26/2011 10:10:33 pm

Thanks for your comments, Mark. However, I actually did say exactly that above: "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). "

The reason I don't recommend a zero-carb diet is because many foods that contain highly beneficial phytonutrients (including vegetables and nuts) contain varying amounts of non-fiber carbohydrates. Also, plant foods that contain fiber typically contain non-fiber carbs as well. While we can get along without carbs, I'd argue that it's healthier to eat a small amount from highly nutritious sources.

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Franziska
9/26/2011 10:21:33 pm

Great website, by the way! And congrats on the weight loss :)

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Mark link
9/27/2011 04:31:28 am

Thanks Franziska for the compliment on my blog - I just started it recently.

I believe you're right on all points in this post. Just wanted to mention the Taubes 'no external carbs needed' point.

From a practical sense, it is near impossible for anyone living in modern society to eat no carbs at all, as Taubes/other suggest.

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Gerri
9/27/2011 06:23:58 pm

Thanks for the great information. I enjoy your posts & look forward to more. As a Type 1 diabetic, I've been adhering to 30-35 carbs daily for over three years to control blood glucose. My body has become quite efficient at converting protein to glucose. Unfortunate that the institutionalized myth prevails about carbs & energy. I've heard the "brain starving" story from healthcare professionals more times than I can count.

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Franziska
9/27/2011 11:38:59 pm

Thanks so much for the feedback, Gerri! Great that carbohydrate restriction is helping to keep your blood sugar in line. Although many continue to prescribe the 130-gram minimum, a good number of doctors and other health care professionals are abandoning this recommendation in light of the favorable research on low-carb diets. I'm sure at some point more dietitians will follow suit -- at least I hope that is the case! :)

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BadMoonT2
9/29/2011 10:20:54 am

I think we go at it in the wrong direction when we start with a number of carbs and then say it's right for everyone. This is clearly not true. As you say some do well on a grain heavy, high carb diet, but a look at the diabetes and obesity statistics hint's that it's not right for everyone.

Luckily our bodies are highly adaptable and if necessary for weight loss or blood sugar control we can do quite well on much lower carb amounts.

As a T2 diabetic I've found it necessary to cut my consumption to the 30 to 50 grams/day level. I've been at it for over 2 years and have noticed no ill effects. My blood sugar improved immediately and dramatically.

I've been really enjoying your well written and well researched blog posts. Keep up the good work! The word needs to get out that low carb is not dangerous and is, in fact, beneficial for many of us.

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Franziska
9/29/2011 11:44:00 pm

Thank you, BadMoonT2! So glad that lowering you've experienced success in lowering your blood glucose with a low carb approach. There are many out there who are eating similarly to you and also having great results, but unfortunately there are lots of others who believe they need 150-200 grams of carbs (or more) in order to be "healthy." Hopefully they will stumble upon this website (or one of the many others that advocate for low carb) so that they can learn the truth.

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Beth
2/29/2012 03:26:55 am

I was so excited to find your blog! I am also an RD who believes in low-carb diets, and I have been feeling very lonely! I began to question much of my nutrition education a few years ago due to a friend introducing me to the Weston Price Foundation and later when I accepted a position where I need to use a low-carb diet on a daily basis. I looked at the research when I began working here, but I feel like I have so much more to learn; so I am going to be following your blog from now on! Thanks so much for sharing your knowledge!

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Franziska
2/29/2012 09:24:57 am

Thanks, Beth! Always great to hear from like-minded RDs. I'm always doing further research on LC diets and realize more than ever that the optimal amount of carbohydrate varies drastically among people. Not everyone should follow low-carb, but for many people it works really well. Feel free to contact me via the "Contact" link with any questions.

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valley girl
6/12/2013 03:49:06 pm

I am 56 & raised in an Eastern European family. Almost in infancy (age 6) school taught us the Holy Grail - the 'food pyramid'. Now I note that preschool is teaching this to my grandchildren. At at 14 I was a little plumper than my best friend; we were exactly the same weight at 7st 12lb & 4oz, but she however was an inch taller than I. I felt fat. There was high protein low carb diet in a magazine called the 'quick teenage diet' which did not dictate a menu just a method and a couple of recipes. However, it warned that it was dangerous to continue for more than 10 days. I did that diet by cutting out bread & minimising potato, pasta & rice at the family meal and eating tinned mackerel for breakfast, which was cheap at the time; but not without much trouble from my father. I felt welI & it worked, & while I didn't weigh myself afterwards, my stomach was flat & I felt good the whole time I ate that way.
I have been on LOW CARB DIET FOR ONLY MY 9TH DAY & I feel good, in fact it brings back the memory that though I didn't have a name for it back when I was 14, I don't feel 'stodgy'. Back then I would have been happy to keep eating that way for the rest of my life. The warning in the diet article & elsewhere, flack from family, 'propaganda' and that's what I choose to call it - the 'food pyramid', interpreted by industry as: grain (& sugar to make it appealing) is the cheap way to fill the populous with a high profit margin - kept me away from low carb until now. Part of that also has been a husband who is not 'into veges' and having a large family on a very ordinary income.
I am just counting carbs (not factoring in fibre - that's new to me from your article) & my average has been 52gm/ day except for the 2nd day when I blew out on fresh home made rye & spelt sourdough bread... my doing, & that day was 125.3gm, I have been aiming for between 50 & 100 mg per day.
There is a strong history of type II diabetes in my family and I watched as my father struggled, even washing the sauce of his baked beans because he didn't want to go on insulin, but refusing to give away bread & pasta. His latter years were bland & unhappy - that killed him before he actually died of diabetes associated everything.
Since my nutrition lectures as student nurse in 1976 it has been a passion of mine, (in fact I truly felt I should've been doing nutrition,) I've bought books & read everything I can get my hands on, but there is so much contradiction, so much misinformation it is hard to get to the truth. Until I read your article I was only going to do low carb for a month at a time because of all the "warnings" to the contrary. Your article has helped me greatly in feeling confident that I'm not doing the 'wrong thing'. I went from 70.4kg to 68.4kg in 4 days. I have no doubt this is fluid shift, but the fact is I do not feel bloated, my mood is lighter, I don't feel hungry, I don't have cravings & don't seem to have any of those irresistible emotional eating bouts that have pIagued me my whole life (usually when I got home from work or got stressed); I don't even care to weigh myself because I feel good. Thank you for the reassurance your blog has given me. When I was a fitness instructor I think the higher amount of complex carbs were fine because I used them up in at least 10 hours of high impact cardiovascular activity. Now I'm older & more prone to injury, It's no longer 'how hard, high & fast,' any exercise is, it's 'live to fight another day'. Thanks to your article I am going to listen to my body & continue low carb as long as it keeps me feeling this good.

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Franziska Spritzler link
6/12/2013 10:41:34 pm

Thanks so much for your comments and for sharing your experience, valley girl! I'm so happy to hear that you're losing weight and feeling good on low carb. I've been low-carbing for over 2 years and truly feel better than ever :) Check out the links page for other websites, including the incredible recipe sites. Also, consider buying one or more of the books in the "Recommended Reading" category on the right sidebar. Keep up the great work, and best of luck to you!

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Michael
3/2/2014 07:17:51 am

Dear Franziska,
Thanks for the terrific blog. I'm a surgeon who has recently lost 55 lbs by restricting carbohydrates. I'm now maintaining my weight at a healthy level by avoiding more than 125 grams of carbohydrates. Anything more seems unnecessary and unnatural. I feel great. It is interesting to see how little evidence there is to support the recommendations for a carbohydrate intake of 250 or more grams per day. Thanks very much for sharing your expertise.

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Franziska Spritzler link
3/2/2014 07:34:19 am

Hi Michael,

Thanks so much for your comments and for sharing your story. Congratulations on losing 55 lbs with carb restriction. I'm so glad you feel so well. Carbohydrate tolerance varies so much from individual to individual, and you seem to do well with a moderately low amount in your diet. Thank you for your support, and I wish you continued good health and well-being.

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Bluewings link
7/27/2014 09:30:25 pm

At long last I have found the answer to the number of carbs for a low carb diet . I am T2 diabetic and using insulin but need to now lose a considerable amount of weight. Thank you for this wonderful website.

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Franziska Spritzler link
7/27/2014 10:08:34 pm

You're most welcome! Thank you for the nice feedback, and best of luck to you.

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Benne the clone
2/24/2015 02:21:41 pm

So great to read this! I have T2 diabetes and have not been that careful about managing it until very recently. Peripheral neuropathy had become so bad for me that I started researching direct links. I couldn't find any, but speculated after some time that diet was directly related to the pain level. After only 3 days on a low-carb regimen (45-60gm/day) I have noted a marked decrease in the neuropathy level. Time will tell, of course, but I am *very* heartened by this.

I appreciate your information and look forward to more reading.

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Franziska Spritzler link
2/27/2015 09:13:08 pm

Thanks so much for your comments and nice feedback, Benne! I'm thrilled to hear that your PN has improved since you cut back on carbs. I hope you're feeling well energy wise and enjoying the many delicious foods that make up a low-carb lifestyle. Be sure to check out my Links section for book and website recommendations. I wish you the best of luck and continued improvement in neuropathy and overall health.

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Laura Taff link
10/8/2015 04:30:46 pm

Question: Does the type of carbs consumed come into play? Does whole grain vs refined matter in this?

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Franziska Spritler link
10/8/2015 07:37:40 pm

Hi Laura. Whole grains contain more fiber than refined carbs and are therefore digested more slowly, so they don't make as big an impact on blood glucose or insulin levels. However, even whole grains are pretty high in digestible carbs, as are starchy vegetables like potatoes. On a truly low-carb diet, these should be minimized or avoided.

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Laura link
10/9/2015 04:26:50 am

Thank you for your reply. I was on a low carb diet once (Suzanne Somers) and for that you could eat carbs but only the whole grain carbs, and only once a day, and not together with protien/fat. I'm trying to get back to low carb mostly because sugar is killing me, probably literally. I feel sick and tired when I eat sugar. When I eat natural sugar like coconut sugar and agave nectar I feel ok. (That's what I put in my coffee.) I just wondered if I still keep it at a low intake (Which obviously I'll have to figure out the right number for myself) is white bread/pasta okay too, or is that just like sugar to the body?

Franziska Spritzler link
10/9/2015 08:37:42 am

Actually, all nonfiber carbs break down to sugar (glucose), including vegetables like broccoli. Whole grains are much higher in nonfiber carbs than vegetables, though. It really is a matter of finding out what works best for you. Grains -- even whole grains like oatmeal -- raise my blood sugar significantly, so I avoid them altogether, along with most fruits other than berries.

Avoiding refined sugar sounds like it will be key for you, and adjust your whole grain and other carbohydrate intake based on how you feel. Best of luck to you!

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Mothertomayhem
4/16/2016 02:28:11 pm

I gained a whopping 85 lbs while pregnant with my son 7 years ago due to my thyroid shutting down at some point during the pregnancy. I lost about 40 of it right away and have struggled with my appearance ever since. I have polycystic ovarian syndrome and am hypothyroidism. Low carb is the only thing that's worked for me, last year I discovered the South beach diet and lost about 15lbs. I unfortunately fell off the wagon and gained it all back. So I am currently back on the phase one which is very carb restricted, day 6 of 14 and I've already lost 10lbs. Do you know of any resources available that list the carb content of common foods? Once I got back to eating carbs I'd like to be better prepared to maintain low intake and make them healthy carbs

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Franziska Spritzler link
4/16/2016 05:49:29 pm

Thanks for your comments and for sharing your story. Congrats on losing 10 lbs in your first week back on low carb!

I really like this carb counter from Atkins: https://files.atkins.com/1512_CarbCounter_Full_Online.pdf.

Best of luck to you with everything!

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roberta
12/17/2016 09:13:17 am

I have done so many diets, it is true not all diets work for everyone, I have friends who thriving on fruits veggies and whole grains stuff like that, I found that to much carb even whole minimally processed dont work to well for me, (metabolic syndrome real bad) I am following a low moderate carb diet, I tried to stay around 150 grams or lower (when I am not craving it to much) first two weeks hardly ate any, my body was okay with it then the cravings hit so I upped to 150 but found this was to low, so I upped it to 200 grams total per day (small amounts in my meals) but now I am finding that I am not reaching 200grams anymore, some days I eat only 100 grams and so far not suffering, not forcing it by the way andnot trying for ketosis,just want to reduce the gluocse load and the damage it was doing to me. right now fighting a cold, for once my infection did not start inmy sinus, but in my throat, and so far it has been mild, I still have some energy (as opposed to times past where any infection wiped me out) I am using immune stuff too, but anyway I have been following this almost 2 months, making my own low carb desserts if I find a need for it, I am happy to report my body seems to like this better than the last couple of times I did low car (did more low caloire low fat diets inthe past was that ever a disaster) I seem to be doing better, but of course only two months and this is experiemental for me. weight loss is not the immediate goal right now I want to see where this takes me and where my body does with it. nothing has worked to improve my health cause permenant weight loss that was actual fat loss not muscle and water loss. time will tell.

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Leo Tat link
1/21/2017 01:59:56 pm

I don’t actively monitor the amount of carbs I eat.

As an asian I used to eat white rice everyday. I just completely stop having rice. I now only eat meat and vegetables (overground). So the main carbs I get are from vegetables, mostly fiber. I guess it should be less than 130 grams (for brain function).

What I have found though is my energy levels are stable through out the day and I am clearer and more focused in contrast to before my diet change. Maybe for me I can be extremely low carb.

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Brynn
10/3/2017 01:13:25 pm

I just wondered, does the fiber being insoluble vs soluble make a difference? I assume fiber is the insoluble carbs, and you said you personally don't count fiber in your total carb intake. I ask because I noticed a package of smoked canned oysters has 10g of carbs, but the oysters contain no fiber. Does that mean all 10g are soluble fiber? Almonds are a bit confusing: 20g of carbs overall in 1 cup, and 11g of fiber. Am I over complicating it? With the almond example, should I just subtract 11 from 20 and count it as 9g of carbs?

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Franziska Spritzler link
10/3/2017 02:11:28 pm

Hi Brynn,

Thanks for your questions. I subtract all fiber, both soluble and insoluble, to obtain the net carb count. Neither soluble nor insoluble is absorbed in the small intestine; therefore, it doesn't raise blood sugar. However, although insoluble fiber contributes no calories, your gut bacteria ferment soluble fiber into short-chain fatty acids, which produce a very small amount of calories (1-2 calories per gram of soluble fiber).

The carbs in oysters are digestible carbs, so they can't be subtracted from the total. Therefore, the package of oysters contains 10 grams of net carb.

With almonds, yes, you can subtract the 11 grams of fiber from the total carbs and count the 9 grams of net carb remaining.

Hope that helps!

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