Adapting to Fat on a Low-Carb Diet

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Adapting to Fat on a Low-Carb Diet

By: Dr. David Ludwig

, Physician, Nutrition Researcher, and Public Health Advocate. Author, #1 NY Times bestselling book ALWAYS HUNGRY?

How long does it take for your body to become adapted to a low-carbohydrate diet? This question has relevance for everyone trying low-carbohydrate diets for weight loss, and also for a raging scientific controversy.

Some critics have pointed to studies lasting just a few days, as evidence that low-carbohydrate diets are detrimental to metabolism. But these studies have a fatal flaw, as it relates to long-term effects.

On a standard high-carbohydrate diet, the brain is critically dependent on glucose. So if you restrict carbohydrate in your diet (or you fast for more than a day), your body must initially break down protein from muscle for conversion into glucose. However, this response is only temporary because over time, the body converts to a special fuel, called ketones.

Ketones are produced directly from fat and have the critical ability to cross the blood-brain barrier and nourish the brain. (Ketones may also have anti-inflammatory, anti-aging, and anti-cancer actions, but that’s another story.)

How quickly does this process of fat adaptation take? At least several weeks. For graphs/charts, please go to:

Owen OE, et al. JCEM 1983, 12:359–379

FIRST: Generally speaking, the most potent stimulus for ketone formation is fasting, since the consumption of anything that could be converted into glucose (carbohydrate and protein) is zero. As this figure shows, the blood levels of each of the three ketones (BOHB, AcAc and acetone) continues to rise for at least 3 weeks. The prolonged nature of adaptation to complete fasting has been known since the classic starvation studies of Cahill 50 years ago. It stands to reason that this process might take even longer on standard low-carbohydrate diets, which inevitably provide some carbohydrate and significant protein.

Yang MU et al. JCI 1976, 58:722–30

SECOND (above): Men with obesity were given a calorie-restricted ketogenic diet. As you can see from the figure, ketones in the urine continued to rise for 10 days through the end of the experiment, and by then had achieved levels only equal to those on day 4 of starvation. Presumably, this process would be even slower with a non-calorie restricted ketogenic diet, because that would inevitably provide more carbohydrate and protein, slowing down the process of converting to ketosis.

Vazquez JA et al. Metabolism 1992, 41:406–14

THIRD (above): Women with obesity were given a calorie-restricted ketogenic diet compared to a non-ketogenic diet, both with the same protein. For 3 weeks, the break-down of lean tissue like muscle (i.e, nitrogen balance, see bottom panel) was greater on the ketogenic diet compared to the non-ketogenic diet, but this difference was completely abolished by week 4.

Hall KD et al. AJCN 2016, 104:324–33

AND FOURTH: In a study by a chief critic, 17 men with high body weight were first given a standard diet, followed by a ketogenic diet. Unfortunately, the study wasn’t randomized, and for many reasons considered elsewhere, was biased against the ketogenic diet. Even so, you can see that for the first 2 weeks on the ketogenic diet (left arrow), the rate of fat loss decreased. But after 2 weeks (right arrow), there was a clear acceleration in fat loss on the ketogenic diet.

Indeed, among the relatively few studies with adequate numbers of participants lasting more than 3 weeks, there is some evidence for an advantage of low-carbohydrate diets for metabolism, and possibly body composition (the relative amounts of fat to lean tissue), but we need more research to know for sure.

The bottom line is that fat adaptation to a low-carbohydrate diet can take at least 3 weeks. During that time, you might not feel quite as energetic as you would subsequently. And if someone tells you a low-carbohydrate diet won’t work based on studies lasting < 3 weeks, tell them you’re going to await higher quality, long-term research.

18 Replies

  • There's not a single study published that shows that long term high fat diet is detrimental

    Only fear mongering words found

    I am on this for more than a year and very comfortable and adapted.

    Really happy to see fasting between 80 to 95 daily which is a good range and entirely depends on what I had the day before

    Also my pre dinner most of the days are around 85.

    Energetic. Slim. Flat tummy. Alert. No more sleepiness. Boundless energy.

    BS under control unless I break off sometimes

    I was fortunate to adopt early after diagnosis.

  • That's great to hear. Thank you for the input!

  • The High Fat dogma of Ancel Keys days sticks like a plague.

    It's all about money.

  • Anup

    I didn't get your point.

  • Food and Drug industry still latching onto Low fat nonsense -- failed diet heart theory -- all for money. Coke with Fiber a new health drink, for example :)

  • I am on this -- high fat -- since six years now :)

    Experts tell me I will have multiple organ failure, but they don't provide any science to validate their distorted opinions. I think i'II will surely have multiple organ failure eating whole grains and hitting 180 PPBS, despite medications, than keeping PPBS to 120 without medications :)

  • @Anup

    "Experts tell me I will have multiple organ failure"..!! Who are these experts ? Utter nonsense. All the exercise to give drugs and getting lab reports done etc are to keep bs in a normal range. If you and all who can do it with diet is the treatment.

    " I think i'II will surely have multiple organ failure eating whole grains and hitting 180 PPBS, despite medications".. You are absolutely right. Even an illiterate person knows that one has to stay away from things / food that don't suit him / her. We can't tolerate carbs so need to stay away. It's not a rocket science but a common sense / understanding.

  • Experts with flashy PG degrees in Medicine :)

  • anup

    And they are the care takers of indian health 😝😝😝. Wrong with our education and health system. Everybody is exclusively after money. Leaders after votes and power. They want cheap popularity and allow medical education to be paid. We are yet to see misfit people in the health. Firstly reservation and now low calibre students. 😝😝😝

  • Much worse nowadays. All private institutions charge heavily for donation for admission to medical college without merit. Such students then become doctors without much knowledge or intelligence to apply that knowledge in real time scenarios. Doctor's son or daughter become doctor by just giving donation to college and wouldn't be performing well then as doctors though with readymade hospitals by their fathers/mothers. In our city, there is a case where admin of college were asking for lot of money for passing the students when they are failing...such a low standard of our education has become!

  • So, isn't that like a bribe to pass everyone that has a parent that's already a doctor, Pinky5?

  • He is under Remand by police now. The things which are not moral and legal come out one day anyway!

  • Pinky5

    Yes. Now the children of rich people say openly that they don't need to work hard after studies. That their fathers has lots of money and they would become doctors.

    These institutions are money fetching / extracting machines. The owners know that the students have lots of money. They also inquire about how rich the parents are. There is money on every stage. Admission, passing exams, to be allowed to sit in exams and on various activities. Now a days in gujarat a person running medical college has been captured for asking 20 lakhs from a student just to allow to appear in the final exams. She is a daughter of doctor parent.

    44 Crores plus cash and cheques worth 101 crores have been captured so far. This guy has invested in properties to a great extent. A poor dentist in 1990 has 10,000 crores worth today ! Earned just from medical / dental college. And we call it progress 😳.

  • believ or not my cousiin was asked 1 crore for MD seat, that too not in main city area but some distant college

  • Sir, I want to have some idea about what your normal meals are like ? as I am still struggling with limited success with LCHF diet

  • Do u eat eggs and or non Veg?

  • My question is for for Shri Shashikantiyengar thank you :)

  • Yes , I eat one egg daily for b'fast and fish occasionally but no other non veg food.I mostly survive on veggies like cauliflower, brinjal, cabbage ,beans, tomatoes ,different types of gourd, cucumber and spinach (twice a week) and a small bowl of daal ,taken with one small roti made of 2 tbsp.coconut flour,1tsp.psyllium husk and 1tsp multigrain wheat flour . I have reduced fruits (which I loved) to just one guava , orange, kiwi or 3-4 strawberries a day .

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