A plant-based, low-fat diet decreases ad libitum energy intake compared to an animal-based, ketogenic diet: An inpatient randomized controlled trial
Contrary to expectations of advocates of low carbohydrate and ketogenic diets, this study did not support the carbohydrate-insulin "carbohydrate/sugar makes you fat" hypothesis. Contrary to the advocates of low fat diets, this study did not fully support the passive overeating "fat makes you fat" hypothesis.
I think this study does support the Meats & Sweets approach, particularly the inclusion of fruits at the expense of very high fat animal products.
Here's the abstract:
The study was inpatient and had a crossover design. None of the 20 subjects had metabolic disease. Each subject was randomly assigned to one of the two diets for the first 2 weeks each diet
Fats and Sugars
The PBLF diet provided 50 g sugar per 1000 kcal. Almost all meals and all snacks included fresh and/or dried fruits.
Fats in the ABLC diet came from meat, poultry, fish, eggs, dairy, olives, avocados, mayonnaise (unknown oil), canola oil, nuts, peanuts, or flaxseeds.
The study report has photos of all meals served, some I have presented below.
The meals were composed primarily of whole foods and subjects ate as much as desired of what was offered. Meal service provided more than 5000 kcal daily for each subject:
Glucose and Ketones
The ABLC was significantly ketogenic:
blood glucose levels were in the normal range on both diets:
- Triglycerides were higher on PBLF than ABLC, but both were within healthy range
- LDL particle size did not differ between the diets
- Uric acid was higher on ABLC than PBLF (7.2 vs 4.8 mg/dL)
ABLC adversely affects thyroid?
This study appears to support previous reports that ketogenic diets may adversely affect thyroid function:
- Thyroid stimulating hormone (TSH) level decreased from baseline on PBLF, but not ABLC, suggesting PBLF improved thyroid function (p=0.03 for PBLF decline).
- TSH was significantly higher on ABLC (keto) than on PBLF: 2.34 vs 1.86 (p=0.009)
- Free (active) T3 was significantly lower on ABLC than at baseline (2.61 vs 3.30, p<0.0001) and compared to when on PBLF: 2.61 vs. 3.13 pg/mL (p<0.0001)
- Total T3 was significantly lower on ABLC than on PBLF: 88 vs. 113 ng/dL (p<0.0001)
This supports the hypothesis that increasing carbohydrate while reducing fat improves thyroid function while simultaneously increasing fat and decreasing carbohydrate impairs thyroid function. Of interest here:
Increased TSH has been reported to aggravate atherosclerosis.
Elevated TSH promotes cardiac arrhythmia
Increased TSH has been reported to increase risk of coronary heart disease and mortality.
Increased TSH in normal range are associated with unexplained infertility.
Increased TSH in normal range is associated with increased thyroid cancer risk.
Hunger and SatisfactionContrary to prediction of carbohydrate-insulin hypothesis, hunger, satisfaction, fullness and eating capacity were no different between the two diets. In other words, eating carbohydrates, including sugars, did not make people more hungry than eating fat.
Energy intakeWhen assigned to the PBLF diet, during the first week, subjects consumed on average almost 700 kcal less daily than when on the ABLC diet. During the second week, subjects consumed almost 600 kcal less on the PBLF diet than when on the ABLC diet. During the second week on the ABLC, the subjects consumed about 300 kcal less daily than during the first week on the ABLC.
Nevertheless, there is a clear trend for a significantly lower total energy intake on the low-fat diet. This is not rocket science. Since people consume about 3-4 pounds of food daily to feel full, if the food eaten has a lower fat content it has a lower energy density, and if your food has a lower energy density your total energy intake will be lower, assuming no great change in total food intake (pounds per day).
Energy expenditureTwenty-four hour energy expenditure was about 166 kcal/day higher when subjects were on the ABLC diet than when they were on the PBLF diet.
Fat balanceWhen on the ABLC diet, subjects lost lean mass (more than 1.5 kg, likely mostly water + glycogen + ?) but little body fat (about 0.25 kg); when on the PBLF diet, subjects lost little lean mass (less than 0.5 kg) and significantly more fat mass (about 0.75 kg).
The subjects spontaneously lost more body fat when eating 50 g sugar per 1000 kcal, compared to when trying to satisfy hunger with fats, mostly animal fats.
The subjects spontaneously lost more body fat when not in ketosis, than when producing substantial ketones.
This is predictable because the subjects had a significantly greater fat intake on the ABLC than on the PBLC. Every gram of fat you eat replaces a gram of body fat as an energy source.
Fat balance = (fat ingested + fat produced onboard) – fat oxidized
If you oxidize (burn) more fat than you ingest and produce (via de novo lipogenesis), then you have a negative fat balance, and you lose body fat.
If you oxidize less fat than you ingest and produce, then you have a positive fat balance, and you gain body fat.
Simply put, the more fat you eat, the less body fat you will burn. To lose body fat, you absolutely must eat less fat than you oxidize.
Regardless of whether your diet is plant- or animal- based, reducing fat is predictably more effective for fat loss than increasing fat. It is just mathematics and economics.
You don't have to eat a plant-based diet to reduce your fat intake. Simply eat animal foods that have a lower fat content, more like wild game than the high fat products produced by modern animal feeding methods.
The main limitations of this study are:
1) Limited duration: Each subject followed each diet for only 2 weeks. This study can't support any conclusions about long-term effects of following either diet. Long term adaptation to either type of diet could result in either increased or decreased energy intake.
2) Inpatient design: This study can't be generalized to free-living subjects making independent food choices. As the authors state: "Due to the controlled food environment in our study, the only choice available to our subjects was how much of the presented foods and beverages to consume."
ConclusionsThe authors conclude:
1) This study did not support the carbohydrate-insulin hypothesis. Although the PBLF diet contained foods with a high glycemic load and significantly increased post-meal glucose and insulin levels compared to the ABLC diet, subjects consumed less energy and lost more body fat when eating the PBLF diet compared to the ABLC diet, opposite of prediction of the carbohydrate-insulin hypothesis.
2) This study did not support the passive over consumption model either. Although the ABLC diet had a high energy density, it did not result in net body fat gain.
A murine study published this year also refuted the carbohydrate-insulin hypothesis.
However, I disagree with the second conclusion of Hall and colleagues. Since the ad libitum ABLC diet did not produce body fat loss whereas the ad libitum PBLF diet did, this tends to lend support to the passive overconsumption model.
The high energy density of the ABLC diet apparently prevented spontaneous reduction in dietary energy intake, whereas the low energy density of the PBLF diet allowed a spontaneous reduction in dietary energy intake.
Since subjects ate ad libitum on both diets, and reported no differences in hunger or satisfaction, this suggests that when we eat high fat foods, we have to eat more total energy (kcal) to achieve satisfaction of hunger, than if we eat high carbohydrate foods. In other words, as has been previously established, this study supports that whole foods rich in carbohydrate and low in fat are more satiating per kcal consumed than high fat animal foods.
In my view, this study provides more evidence that if you want to control body fatness, you should focus on controlling dietary fat content, not dietary sugar. You should reduce butter, cream, other animal fats, including fatty meats, and especially eliminate plant-based oils, not fresh or dried fruits or honey.
This study also supports my hypothesis that we are by Nature designed to eat both natural sweets and lean meats.
By natural sweets here I mean low energy density whole sugar-rich foods – primarily fruits (fresh, dried and juiced) and honey – to satisfy hunger and provide a large part of our energy requirements. In other words, meats and sweets.
As I presented in The Hypercarnivore Diet, we have multiple adaptations to a highly carnivorous diet including:
- Shoulder girdle adapted to hunting by throwing projectiles with high accuracy
- Stomach acidity similar to scavengers/carrion eaters
- Ability to digest bones
Lean meats provide essential protein/amino acids, fats and micronutrients in a non-toxic package. Presumably we are best adapted to lean meats having a low fat content similar to wild game.
However, we also have features of frugivores, including:
- General gut structure similar to other frugivores
- Color vision and visual acuity (felines and canines are comparatively color blind) for identifying ripe fruits
- Ability to taste and high preference for sugars (absent from carnivores)
- Sugar dependent large brains (What really made primate brains so big?)
- Adaptation to tannins via salivary proline-rich proteins (page 10)
Hence the hypercarnivore upgrade: Meats & Sweets: The High Vitality Diet