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Quick Summary tl;dr
This study investigated whether low-carb eating could improve Metabolic Syndrome independent of weight loss, as compared to calorie-controlled diets lower in fat and higher in carbs.
The low-carb diet decreased triglycerides, increased HDL, and improved LDL better than the medium-carb and high-carb diets, and in just four weeks.
The low-carb diet reversed Metabolic Syndrome in 9 of the 16 participants. The lower fat high-carb diet only did so in 1 of 16.
Low-carb and ketogenic diets have many proven metabolic benefits, including improving insulin sensitivity and reversing diabetes or decreasing triglycerides and increasing HDL. However, some stipulate that the metabolic benefits associated with ketogenic diets are a consequence purely of weight loss.
So, the following question arises: is there a metabolic advantage of eating low-carb that exists independent of weight loss, as compared to eating a low-fat or moderate-carb diet?
Calorie-Controlled, Low-Carb, Medium-Carb, and High-Carb Diets
To answer this question, researchers ( Hyde et al, 2019) took 16 obese individuals and put each on three separate 4-week long calorie-controlled, weight-maintenance diets: low-carb (LC) [6% carbs], medium-carb (MC) [32% carbs], and high-carb (HC) [57% carbs]. The high-fat LC diet was richer in animal products and the low-fat HC diet included five servings of fruits and vegetables per day.
The macronutrient details of the diets are shown in Table 1, copied below. All diets were, on average, 2,950 Calories (green), and energy from carbohydrates (yellow) was swapped for energy from fat (orange). Therefore, the LC group ended up eating over 3-times more total fat and 2.5-more saturated fat. Remember that for later.
Metabolic Syndrome
Importantly, each of the study participants also had Metabolic Syndrome, a conditioned that affects 1 in 3 American adults and is defined by the occurrence of at least three of the following five features: a large waistline, high blood pressure, high triglycerides, low HDL cholesterol, and high glucose. Metabolic Syndrome, as its name suggests, raises a person’s risk of developing other metabolic diseases, including heart disease, diabetes, fatty liver, and Alzheimer’s disease, to name just a few.
Benefit 1: Decreased Triglycerides
Triglycerides are fat in the blood. Therefore, you might think that eating fat would raise triglycerides more than eating carbs. Fat is fat, after all, and carbs are not. However, it’s not so simple. On a low-carb diet, fat burning increases and more fat is pulled from the bloodstream. Conversely, on a high-carb diet, carbs are turned into fat via a process called de novo lipogenesis.
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On the high-fat LC diet, triglycerides decreased by a substantial 32% from baseline, whereas on the low-fat HC diet, they increased by 12%. Also, despite the fact that the average participant ate 2.5-times more saturated fat on the LC diet as compared to the HC diet, they had much lower levels of saturated fat in the blood.
Literally, the group eating more bacon, butter, eggs, and heavy cream, and less fruits and vegetables, had lower levels of saturated fat in their blood. That’s not medical advice, but it is a fact.
A low-carb diet with bacon and eggs led to 32% lower levels of triglycerides (fat) in the blood. An isocaloric high-carb diet increased triglycerides by 12%.
Benefit 2: Increased HDL
HDL cholesterol particles can clean up blood vessels and have antioxidant properties. High HDL is good and protects against heart disease. In my opinion as a PhD scientist and metabolic health practitioner, I’d much rather have a high HDL than a low LDL any day. And, fortunately for my fat-loving palate, HDL was significantly, 18%, higher after the LC diet than it was after the low-fat HC diet.
A low-carb diet leads to higher good HDL cholesterol than a low-fat diet.
Benefit 3: Decreased Small Dense LDL
LDL unfairly has a bad reputation. LDL can contribute to heart disease once it’s become small and dense, which tends to happen when there’s more sugar in the diet. Pattern A LDL is characterized by very little small dense LDL, whereas pattern B is characterized by more small dense LDL. Pattern B LDL contributes to heart disease, so you want to be pattern A, not pattern B.
At baseline, only 3 of the 16 participants were pattern A. But after the LC diet, 9 were pattern A. The low-fat HC diet only turned 1 participant from pattern B to A. Importantly, this change was independent of change in total LDL. In other words, total LDL did not change significantly as the result of any of the diets, but the type of LDL became better when fewer carbs were eaten.
Cutting carbs improves LDL. This doesn’t mean it decreases LDL, but that it prevents LDL from becoming small and dense.
Benefit 4: Reversed Metabolic Syndrome
After just four weeks, the high-fat LC diet reversed Metabolic Syndrome in 9 out of the original 16 participants. It’s possible, or even likely, that all 16 would have successfully reversed Metabolic Syndrome had weight been allowed to naturally decrease or had the study duration been longer than one-month. By comparison, only 1 of the 16 participants reversed Metabolic Syndrome after the low-fat HC diet.
A low-carb diet reversed Metabolic Syndrome in 9 of 16 participants in just four weeks, independent of weight loss.
Conclusion
This study revealed that a high-fat low-carb diet has metabolic advantages that are independent of weight-loss and can be observed in only 4 weeks.
It is important to note that all studies have limitations. For example, the population in this study had pre-existing Metabolic Syndrome. Therefore, one cannot conclude that a low-carb diet is best for metabolically healthy people. However, given that 1 in 3 American adults has Metabolic Syndrome and 88% are metabolically suboptimal and at risk of developing Metabolic Syndrome, the data may be generalizable to a large proportion of the population. ( Araújo et al, 2019)
Furthermore, the study included only 4-week interventions. In this time, the low-carb diet was able to decrease triglycerides, increase HDL, improve LDL phenotype, and reverse Metabolic Syndrome better than the isocaloric medium-carb or high-carb diets. But it is possible that had the participants remained on the low-carb diet longer, more benefits would have been observed. In fact, by the end of the 4-weeks of low-carb, other positive trends were already being observed such as decreased liver fat, decreased blood pressure, and improved insulin sensitivity.
Imagine what might have happened to participants had they been allowed to lose weight and stay on the low-carb diet for more than one month?
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