Your Dr. friend wasn’t sufficiently fat adapted.
I frequently row over 10k and put it a 1 hr. HIIT workout while fasting—on the same day. I never “hit the wall” when I’m fasting/keto, only if I eat carbs.
Best part—I lost 50 lbs, kept it off for two years and counting and my life-long asthma is gone.
The carb versus fat diet has been a contention for a while. Each side has its points. Personally, I can’t use the low carb diet because of medical conditions that require carbs. And that balance can’t be reached within the keto guidelines. I’ve had great success with modifying the Harris Benedict Formula and I’ve lost a lot of the weight I gained from intense steroid use for many years and been able to keep that balance of blood sugars being unable to exercise now do to a number of other health triggers.
Additionally, there might be a long term effect with low carb as research found those with low carb diets died an average of four years earlier than those with moderate intakes. Even people with high intakes fared better than those who cut out carbohydrates.
“Low-carb diets that replace carbohydrates with protein or fat are gaining widespread popularity as a health and weight loss strategy,” said study leader Dr Sara Seidelmann, from Brigham and Women’s Hospital, Boston. “However, our data suggests that animal-based low carbohydrate diets might be associated with shorter overall lifespan and should be discouraged.
For the study, which was published in Lancet Public Health, researchers followed 15,428 adults aged 45-64 over two decades from 1987. The researchers found that, from age 50, average life expectancy was 83 years for those with moderate carbohydrate intake (50-55 per cent of daily calories), which was four years longer than those with very low carbohydrate consumption (less than 40 per cent of calories) who lived an average of 79 years. Those with a high carb intake (greater than 70 per cent of daily calories), lived until an average age of 82.
Another study I looked at also provided that a high fat diet is being related to insulin resistance which induces the retention of trunk fat. The study also indicated that high fat diets contribute to the development of chronic non-communicable diseases (NCDs), such as obesity, hypertension, and chronic kidney disease (CKD) .
https://www.frontiersin.org/articles/10.3389/fnut.2019.00060/full
So there’s something to say on both sides of the argument. Wish you good health.
Wy69