Let’s talk about hypoglycemia and fasting. Do you have trouble making it through a 12-hour fast? When you fast for a medical test, can you comfortably make it twelve hours without that hypoglycemic feeling?
In my 20’s, 30’s and 40’s I had trouble fasting for medical tests. I suspect I never noticed it in my childhood because I didn’t have many blood tests. I also didn’t give much notice to how much or when I ate. I was/am fortunate to not be overweight.
Looking back on my diet growing up and in my first several decades, my very high carb intake probably did not help my metabolic flexibility. I became reliant upon a certain amount of carbohydrates to maintain my blood sugar. I was an athlete and needed a lot of calories. I suspect my muscles were insulin sensitive- a good thing, but overall, I was not metabolically flexible. I remember thinking if I was ever stranded on an island without food, it would be a very bumpy time getting my body to that point of adaptability when hopefully, I would be producing ketones so I could hunt and gather to survive.
The low carbohydrate, low fat diet comparisons have been around since the beginning of nutrition science-hundreds of years. It forms the basis of understanding our ancestor’s diets. Perhaps it’s my sports nutrition background but macronutrient ratios are a topic I’ve long taken an interest in.
Part of the intent of this study was to look at the effects of carb/fat ratios on hunger, appetite and weight. As is true with so much of research, these results suggest that this study needs to be longer. Nutrition can not be encapsulated in two weeks. It’s a start but results can in no way reflect what occurs in the body in six months or in over a year.
This was a crossover study where participants ate low fat or low carb for two weeks and then switched over. People on the low-fat, plant-based diet ate fewer daily calories but had higher insulin and blood glucose levels, compared to when they ate a low-carbohydrate, animal-based diet. The lower fat diet resulted in weight loss because they ate overall fewer calories, though the lower carb vs higher fat did not result in weight gain.
This study also further demonstrates the point of my book, The Seductive Land of Carbs, which I wrote five years ago. My big question is what is the optimal carbohydrate intake for each person that will satisfy a healthy gut microflora and maintain metabolic health?—and yes, the two are connected.
Not everyone will see their cortisol levels rise on a low carb diet and not everyone will see their cholesterol lower on a low fat diet.
Optimal carbohydrate intake is not black or white. Many factors influence a person’s response to the amount of carbs in their diet including, genes, gut microbiome, type of carbohydrate, physical activity and medical history.
In regards to the study results, the obvious question is what happens with those higher glucose and insulin levels over time?
I talk a lot about this topic with my clients. It’s also a recurring topic in my system biology course. Unfortunately most of the research on low carb vs low fat focuses on energy utilization and not the gut microbiome influence as if the two are mutually exclusive.
As you help your clients balance the type and amount of carbohydrates that best suits them, keep in mind that we must be careful of our own personal bias. Each of your clients will be unique in their response.
For most people it’s more about eating a low—ER amount of carbs and balancing carbs that are more nutrient dense. Maybe it’s 100 grams, maybe it’s 150 grams maybe its 75 grams or maybe the person is more active and can eat much more— still, all while paying attention to glycemic index/glycemic load because these usually correspond with nutrient density.
Good Rule of Thumb: First figure out optimal protein needs, which are based on estimated ideal body weight, (not current weight), age, physical activity and state of health. Usually optimal protein ranges from .8-2 gram/kg IBW. Then work carbohydrate and fat amounts around optimal protein intake.
Metabolic Flexibility
When we jostle the ratio of macronutrients we are tuning into metabolic flexibility. This is a concept I learned decades ago in my sports nutrition days. It is based on the idea that as we lower carbohydrates and raise fats, energy utilization changes. Metabolic flexibility essentially is the ability to utilize various energy substrates (carbs, protein and fat) as our needs and environment change. I believe you can be insulin sensitive but metabolically inflexible; better to be both.
The ratio of the macronutrients is the basis for the fasting mimicking diet. Bump up the protein, carbs or calories too much, you start to secrete more insulin and fall out of ketosis and autophagy.
When 55 % or higher of our diet is always from carbohydrates and especially refined, low nutrient carbs, then our liver and pancreas can get out of sync with gluconeogenesis, glycogenolysis, and fatty acid oxidation-especially in the absence of physical activity. Even the leanest person has fat stores to burn. And an obese person has a surplus of adipose stores. It’s how effective you are at tapping into them—part of metabolic health.
Easily becoming hypoglycemic on a high carb diet, even in the absence of diabetes is a sign of metabolic inflexibility. Most healthy people should be able to comfortably fast for 12 hours.
Keep in mind, carbohydrates is the only macronutrient where there is no official recommended amount. Fat and protein are different. We develop signs of deficiencies and malnourishment when fat and protein are inadequate.
There are many great references and researchers on this topic including the pioneers, Stephen Phinney and Jeff Volek, but also David Ludwig, MD, and Eric Westman, MD. However, even their research has a more targeted focus on energy utilization and doesn’t raise the variable of the gut microbiome. Carbohydrates and diet have an enormous effect on gut flora and the subsequent potential for insulin resistance because of dysbiosis and the possible presence of more pathogenic organisms.
Although I realize these two questions do not live in isolation, still —two very important questions:
1. What is an adequate amount and type of carbohydrate in a person’s diet to maintain a healthy gut flora?
2. What is the optimal amount and type of carbohydrate for a person to maintain healthy blood glucose levels and metabolic health?
Are these two questions related?
Do we know what is that amount for any one individual?
Here is an experiment that I ask of all my clients who do not take exogenous insulin (keep in mind,some of these rules can be applied to type 1 diabetics too, but with caution). I ask my clients to fast for 12 hours and make note of how easy or not it may be. And make note of your diet the day before. How high carb and how high calories is it?
Sometimes what we believe is our norm is really something else that can be positively changed to a healthier state.
Finally, I suspect we can toss into the debate gene snps related to inflammation, glucose regulation and nutrient absorption. How our body responds to the macronutrients is not black and white. Each person’s unique gut microflora and genetic make up make sure of that.
