Maybe Low-Carb Diets Are So Effective Because They Alter Gut Bacteria

Details are in The International Journal of Obesity.


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17 responses to “Maybe Low-Carb Diets Are So Effective Because They Alter Gut Bacteria

  1. Nick

    I just stumbled upon your website yesterday and am going to buy your book on the ketogenic med. diet and follow your blogs. My mother and I have been on a very low ketogenic diet for about 7 months (as a vegetarian I personally eat mainly the types of cheeses you recommend, eggs, whey, butter/unsaturated fat and a little vegetables – and additional vitamines and minerals). I try to stay under 20 grams of carbs a day (more often much less than that) and eat about 60 to 80 grams of proteins a day. We have lost a lot of weight (all though much less than these diets promise).
    Every low carb. book tells me I will increase energy. Unfortunately for my mother and I it is the exact opposite. We have been waiting for ‘the miracle to happen’ but we only have a little bit more energy than at the start of the diet. I have some time off, but if I did not I would not have been able to keep following this diet because I am tired alle the time, feel completely depleted, have a very hard time concentrating and often cannot even come up with the right words. I had to decide recently to start cutting the diet temporarily if I want to do anything intellectualy demanding or even mildly demanding. My mother has the same problem. Could you tell me why this could be? Sticking to about 20 grams of protein a day instead of less seems to make no difference at all so we tend to stick to the strict version, as that increases loss of weight many times in comparison to just a bit more carbs. My mother has been tested for diabetes and is not. Her liver, kidney, cholesterol, thyroid etc. all are all okay. Hope you can help. If it weren’t for the serious lack of energy, I would stick to a low carb diet for life. It suits me just fine and it is actually the only diet that does exactly what it says it does for your weight. And we are never hungry – and never have cravings.

    • Hi, Nick.
      Problem could be a vitamin or mineral deficiency, or you’re genetically not able to use ketones very well for energy. About 50 other things could be going on. 20 grams of protein a day wouldn’t be enough for any adult of average size. Be sure to check with your personal doctor.


  2. Tim

    I would love to see a more in-depth distillation of this study.

    I have been on a recent journey to improve my gut microflora through the use of resistant starch (RS). RS has the unique ability among foods to reach the colon unscathed and is used as a food source for the colonocytes lining the colon. When your gut microflora gets used to a steady supply of RS, it produces a constant supply of butyrate (SCFA). It’s the SCFA which provide fuel for the colonocytes. Starved of fuel, colonocytes begin to shut down, taking with them the ability to control blood glucose efficiently. Well-fed colonocytes give supreme glucose control.

    My experience has shown it takes about 10-20g of RS per day to get into a zone of healthy colon bacteria/SCFA production/glucose control.

    I use mainly potatoes for RS. RS is found in high levels in raw potatoes, cooked and cooled potatoes have about 1/10th the amount as raw, and cooked and hot potatoes about 1/20th. Another good source is very green bananas.

    As an example; 20g of RS can be had by eating 1 small green banana, 1 1″ slice of raw potato, and about a quarter-pound of cooked and cooled potato (as potato salad).

    Results are astounding and seen in 1-2 weeks. Fecal changes occur, then glucose control. A diet of only potato for 5 days will put one in deep ketosis from the SCFA.

    • Trish

      Tim – in view of the fact that potatoes come in many shapes and sizes – can you please tell me what your 1″ slice weighs? I’m trying to relate this to info here for raw potato.

      I’m also interested in whether you need to consume RS over the whole day as opposed to just one meal.

      I thought I was doing well with my breakfast cereal (Goodness Protein 1st) which gives 1,8gm RS per 100gms!!! I’m not so impressed with it now!!

      • Tim

        I’ve read hundreds of papers and articles on RS. Most agree that an optimal amount would be 20-30g/day. The Standard American Diet provides about 3-5g/day.

        There is a company called National Starch which makes a product called Hi-Maize, it comes from a specially bred corn plant that contains a significant dose of RS. They are marketing it as an additive for bread and pastry to increase RS. Many studies use Hi-Maize as their RS source. However, many savvy dieters have given up most grains and don’t eat commercially prepared breads and pastries. If you search for studies on RS, you will see they may have been funded by National Starch or use Hi-Maize as RS. Don’t let this dissuade you, RS is crucial to gut health and can be had with non-grain foods.

        If you wish to increase RS to a level well above the SAD, I would recommend eating these foods: very green bananas, cooked and cooled potatoes and rice, raw potato, raw (unmodified) potato starch.

        If you use the potato starch, you need to eat it in it’s raw state, ie. don’t use it in cooking, just add it to a smoothie or similar method. Raw potato starch is 78% RS by weight–the best bang for your buck if targeting RS specifically. Hi-Maize is only 50% by weight for comparison.

        Potatoes and rice have a unique property in their starch in that when cooked, the starch swells and becomes water soluble–totally NOT RS. But when cooled, the starch ‘retrogrades’, or crystallizes, into RS. This is why sushi rice and potato salad are better choices than fried rice and baked potatoes.

        To keep a good balance and make it easy, I have adopted an approach that uses many methods. I prepare and eat potatoes most days. After cleaning and slicing them for cooking, I eat ‘1 or 2’ slices of raw potato, probably 10-20g worth, or about 1/8th of an average size potato. I then cook the potatoes and have a serving with my meal. The leftovers are refrigerated and eaten cold the next day. In this fashion, you get about 10g RS from each 1/2 pound potato. I also make it a habit to eat sushi or cold rice a couple times a week, and I buy the greenest bananas I can find and eat one almost every day.

        Green bananas are an interesting food. They definitely don’t taste very good, but contain about 15g RS per average sized banana. As they ripen, they lose all of the RS. As long as there is some green, there is some RS. There is actually a ‘green banana diet’ sweeping Japan, the success is thought to be the RS.

        Anyway, RS is easy to study on your own. Go to Google Scholar, PubMed or just Google and type in search terms like: Resistant Starch and obesity, Resistant Starch and Butyrate, Resistant Starch and diabetes, or any other combo…you will be amazed at the studies done and surprised by how little attention this has gotten by the general public.

        Good luck!

      • I appreciate the details, Tim. If memory serves me, raw potatoes have much more of the potentially toxic glycoalkaloids typical of the nightshades. Granted your not eating very much raw; 10-20 grams/day seems unlikely to be harmful. I bet you’ve already confronted this.


    • That’s interesting, Tim. I confess I don’t know much about resistant starch yet.

  3. Tim

    This is a really good study on RS by a respected diabetes organization.

    If you are a carb-counter, and don’t eat rice and potatoes, I would recommend using 1-2 TBS of raw, unmodified potato starch in a smoothie or 1-2 green bananas a day in a smoothie.

    I usually eat green bananas ‘straight’, but they take some getting used to! It’s more bearable if you eat them along with a drink, like coffee, and take a bite and use the drink to help you chew and swallow–you’ll see what I mean the first time you try! Included in a smoothie, green bananas are undetectable. Smoothies can be simply made with any carb content or no carbs at all. Water, ice, and a green banana blended in a blender works well. Add a tsp of potato starch and you have a super RS smoothie.

  4. Trish

    Tim – thanks very much for both your replies! I was searching with other terms and didn’t find what I was looking for – this – ….Raw potato starch is 78% RS by weight… Tried out a small (10gm) section of raw potato cubed with other food – and it’s quite acceptable! (It was my first potato for 3 years!!) So I’ll give the green bananas a miss. They don’t sound too appetizing at all;-) Your link above has fantastic info too – it’s a wonder I haven’t seen it before during my T2 research!! Thanks for that!

  5. Tim

    Click to access ALDfinal.pdf

    Here are two of the best papers I’ve seen on RS. The first is a comparison of RS intakes in US and Costa Rica, the subject may not interest you, but the research on RS is impeccable. The second paper is also very in-depth, and table 2 shows RS content of various foods, and is where the 78% for raw potato starch was obtained.

    Raw potato starch is also known as ‘native’ potato starch. There is also a modified version of potato starch, but I don’t think it would be a good source of RS, it is used in baking processes. Native (unmodified) potatoe starch is extracted at low temps and dried, never changing the structure of the starch that is present in a raw potato.

  6. Trish

    Thanks! Much appreciated!

    • Tim

      Don’t know if you are still following this, but I recently found an answer to a question I’ve had for quite some time. Plantains are essentially bananas, I’ve wondered about their RS content and found it here:

      Turns out raw, unripe plantains are over 50% by weight RS. That is huge! Here’s what I’m trying this weekend:

      Eaten straight, they are inedible, so I took some raw, green plantains, cut them into 1/8″ or so slices and put in a dehydrator. Let them dry until crisp and eat them like potato chips. Very good! Even w/o salt they are fine. Kind of like communion wafers–no taste. With a bit of salt they are very tasty.

      With the water removed, I would guess they are probably 80-90% RS as eaten. Next step is to weigh them, I don’t have a scale that weighs grams. But what an easy way to get RS!

      • Trish

        Still here;-)
        I looked them up on this site – no mention of starch in the list though raw potato and banana both have starch listed! Strange!
        BTW – couldn’t you do the same with thin potato slices? I have made potato ‘chips’ with thin slices in a microwave that are very ‘moresome’ even without salt but obviously that cooks them. I don’t have a dehydrator to try it out.
        Have been trying out raw potato and monitoring my BG levels (my primary focus) – good results so far but it’s hard to measure differences accurately since food intakes vary anyway and I can have flucuatations as much as 1-2mmol after eating exactly the same meal!

        A good general info article here without all the tech jargon

      • Hey, Trish.
        Be aware that the nutrient database at NutritionData is probably outdated. They use USDA version 21 whereas 25 is the current version. Most folks don’t know that. I’m sure it doesn’t matter for many items. You can go straight to the USDA Database:


  7. Tim

    It is hard to find data on plantains. I think they are kind of considered a third world food or something.

    Thin potato slices are OK, too, but they dry very hard and aren’t that great to eat. The plantain slices are crumbly and crunchy and make good ‘crackers’ to eat plain or spread stuff on.

    I recently stumbled across something that has lowered my FBG by nearly 25 points! I found if I eat little to no meat (protein) with my evening meal, my normal FBG of 110 drops to 85. I am experimenting a bit, but it seems if I eat all or most of my daily meat at lunch instead of dinner, it has a drastic effect on sleep quality and FBG. Not sure if you are working the FBG angle, but thought it worth mentioning since you are obviously testing BG at home.

    My email is if you’d rather communicate that way!

  8. Trish

    What a great site! Thanks Steve!