Let me start by saying that I would have written almost exactly what Dr. Layman said in that presentation 3 years ago. I also still tend to hold to the axiom that one should “consume glucose to match the use of glucose as fuel”. In other words, eat only the amount of glucose that will equate to the daily amount of your calorie expenditure that it fueled by direct glucose oxidation, rather than by glucose after it has been turned into fat.
There are a few things that have “shifted” my views however. Some is due to my understanding of the effects of fat and protein on insulin levels that I have seen since my son was diagnose with type 1 diabetes 3 years ago, as well as communicating with around 100 or so type 1 diabetics who are sparking new research due to their observations of the effects of fat and protein on insulin “needs”. Some has also come from myself, and from the emerging research on leucine.
Just a few starter points.
- When type 1 diabetics have alternated between 55-60% carb/25-30% fat diets and 25-30% carbs/55-60% fat diets what has been found repeatedly is that they require only slightly more insulin to manage the high carb diet than the high fat diet at equal calories. The high fat groups become less sensitive to insulin on a unit per unit basis in terms of clearing glucose rises from a meal because a) the elevation in blood lipids from the meal reduces the ability of insulin to move glucose into cells and b) the muscle cells become fat loaded and have less free capacity to store glucose in short order, and c) muscles down regulate glycolytic mechanisms (enzyme) and so lose the capacity to utilize glucose for fuel as quickly. This is not bad for glycemia, but it does mean that replacing carb calories with fat does not proportionately decrease insulin secretion needed to manage a meal. In fact, in general 1 diabetics need the same amount of insulin to manage a 500 calorie meal with 40 grams of carbs (32%) as with 80 grams of carbs (64%) after the first 2-3 days, and the 40 gram carb meal group will need far more insulin if they suddenly introduce an 80 carb gram meal because of down regulation and fat loading phenomenon. This remains true into ketosis as type 1 diabetics who utilize nutritional ketosis tend to need 2-3 times as much insulin per gram of carbs consummed, but at that level the carb intake is so low that total insulin requirements drop. Consuming fat alone raises insulin secretion because it creates a mild resistance to circulating basal insulin and to the liver will put out more glucose than otherwise, and 30% carb dieters (non diabetic) tend to have fasting blood sugar 10-20 points higher than 60% carb dieters on a maintenance level diet. This is the result of so-called physiological insulin resistance. Type 1 diabetics and non diabetics however produce much lower post prandial blood sugar peak levels on a low carb diet because the glycemic curve is extended over several more hours due to the fact that fat slows down absorption. So a 30% carb meal provides a slow release of glucose and amino acids into the bloodstream over 4-8 hours (tested empirically) which a low fat meal provides a fast release of glucose and amino acids into the bloodstream that is DONE within 4 hours maximum.
(A point to the OP then, two larger carb meals (80 grams) with high fat are virtually equivalent to 3 smaller ones because the fat simply extends gastric emptying and absorption time of the carbs proportionately longer).
The big advantage in 30% carb, 50%+ fat then is not a reduction in insulin secretion, nor in average blood sugar, but in glycemic variability. The low carb eaters may range from 85-110, while the high carb eaters may vary from 70-130. The first case is probably healthier. Outside of ketosis, the nervous system must use about 20%-30% of daily maintenance calories in the form of carbohydrate, and will take it from protein if it is not consumed, hence my “consume glucose to match the use of glucose as fuel”. The doctor however understates the bodies use of glucose for fuel during exercise. On a 2000 calorie diet, about 125 grams of glucose will be used directly by the nervous system each day. On a high fat diet, with 125 grams of carbs, the body will adapt to use nearly 100% fat at resting levels and will store it in muscles to do so. At high workloads however, it is not possible to beta oxidize fat fast enough to optimize work output. At about 600 cals/hour, a low carb 170 pound male will burn about 60 grams of glucose an hour (40% of energy) just just to maintain that pace, and the requirements rise as glycogen gets depleted. A high carb dieter will use about 90 grams of carbs an hour (60%). Fat can not be oxidized fast enough to maintain high levels of output above about 6-7 mets without glucose supplimentation. In fact at about 6-7 mets, fat oxidation is topped out and ALL additional energy needs must be met with glucose. At 900 calories per hour for example. the 170 pound low carb athlete will be oxidizing 150 grams of carbs per hour and will only be burning a hair more fatty acids than at 600 calories per hour. Fat burning simply tops out at about 350-400 calories an hour for this standardized athlete. True, a high carb dieter will turn to glucose faster, and top out lower, about 240-300 per hour , but they will both be using almost 100% additional marginal glucose above 600 cals/hour.
Since fat extends the absorption time for amino acids rather dramatically, I believe that it is not possible to spike leucine levels with a high fat, high leucine meal. The fat will smear out leucine absorption and clearance to 4+ hours. Just as the high fat diet reduces glycemic variability, it also reduces amino acid spikes and troughs. Recent Harvard studies have shown that it may take 12 hours to clear blood amino acid levels after a high protein.high fat meal. (Cheese was used). A low fat high protein meal results in protein clearance in about 4 hours confirmed by glycemic studies. Also, amino acids themselves require almost half the insulin per gram to clear as carbohydrate, and leucine requires even more than that-nearly as much as glucose.
Fatty liver is less tied to carb intake and more tied to fructose intake. Unlike glucose, fructose (and alcohol) MUST be turned into triglycerides if they are in excess because. This is because fructose is 100x more glycosylating that glucose due to backing up the pylol (sorbitol) pathway.
Just some things to consider and discuss. I will say, in direct response to the OP that 80 grams of carbs combined with a high fat meal is going to enter the bloodstream slowly. 1 large high fat meal probably acts similarly to two smaller high fat meals if the carbs are increased proportionately, and also if you are weight training, you easily burn through 75 grams of glucose in an hour no matter how fat adapted you are. I have taken in 75 grams of carbs (2 scoops Plasma) and trained an hour and tested my blood sugar every 30 minutes for 3 hours and never exceeded 110 though I did end up in the 60s after 2-3 hours without additional food.