Recent research published in Cell Reports Medicine from the Centre for Nutrition, Exercise, and Metabolism sheds light on the health impacts of different diets. This 12-week study involved 53 healthy adults who followed one of three diets: a moderate sugar diet (control), a low-sugar diet (less than 5% of calories from sugar), or a ketogenic (keto) diet (less than 8% of calories from carbohydrates). The study’s findings are crucial for anyone considering these popular dietary approaches.

Keto Diet and Cholesterol: A Double-Edged Sword

One of the most striking findings from the study was how the ketogenic diet affected cholesterol levels. Participants on the keto diet experienced a notable increase in cholesterol, particularly in small and medium-sized LDL particles. These particles are more likely to contribute to plaque buildup in the arteries, which can lead to cardiovascular diseases like heart attacks and strokes.

Furthermore, the keto diet increased levels of apolipoprotein B (apoB), a protein that is a key component of these LDL particles. Elevated apoB is strongly associated with a higher risk of heart disease.

In contrast, participants on the low-sugar diet saw a significant reduction in LDL cholesterol levels, suggesting that reducing sugar intake, rather than overall carbohydrates, may be more beneficial for heart health.

Expert Insight:

Dr. Aaron Hengist, the lead researcher, expressed concern over these findings, stating, "Despite reducing fat mass, the ketogenic diet increased the levels of unfavourable fats in the blood of our participants, which, if sustained over years, could have long-term health implications such as increased risk of heart disease and stroke."

Impact on Gut Health: The Keto Diet’s Drawback

The study also examined how these diets affected the gut microbiome—the complex community of bacteria in our intestines. The keto diet significantly altered this microbiome, particularly by reducing levels of Bifidobacteria, a type of beneficial bacteria often found in probiotics.

Bifidobacteria play an essential role in health by producing B vitamins, inhibiting harmful bacteria, and lowering cholesterol. The reduction in Bifidobacteria on the keto diet was likely due to a sharp decrease in dietary fiber intake, which dropped to about 15 grams per day—half the recommended daily intake.

In contrast, the low-sugar diet did not significantly affect the gut microbiome, suggesting that reducing sugar doesn’t harm gut health as drastically as cutting carbohydrates does.

Impact on Gut Health:

Dr. Russell Davies, who led the microbiome research, highlighted the potential long-term consequences: "Dietary fiber is essential for the survival of beneficial gut bacteria like Bifidobacteria. The ketogenic diet reduced fiber intake to around 15 grams per day, half the NHS-recommended intake. This reduction in Bifidobacteria might contribute to significant long-term health consequences such as an increased risk of digestive disorders like irritable bowel disease, increased risk of intestinal infection, and a weakened immune function."

Glucose Tolerance: Keto’s Mixed Results

The ketogenic diet also had a notable impact on glucose tolerance—how well the body manages blood sugar. On the one hand, the keto diet reduced fasting glucose levels, which could be seen as beneficial. However, it also reduced the body’s ability to handle carbohydrates, a condition known as reduced glucose tolerance.

Reduced glucose tolerance could lead to insulin resistance, where the body’s cells become less responsive to insulin, the hormone that regulates blood sugar levels. This could pose a risk if individuals on a keto diet decide to switch back to a higher carbohydrate intake.

Adaptive Response and Risks:

Professor Javier Gonzalez explained, "The ketogenic diet reduced fasting glucose levels but also reduced the body's ability to handle carbs from a meal. By measuring proteins in muscle samples, we think this is an adaptive response to eating fewer carbohydrates day-to-day. This insulin resistance is not necessarily a bad thing on a ketogenic diet, but if these changes persist when people switch back to a higher carbohydrate diet, it could increase the risk of developing type 2 diabetes in the long-term."

Fat Loss Success with Both Diets

Despite these metabolic changes, both the ketogenic and low-sugar diets were effective for fat loss. On average, participants on the keto diet lost 2.9 kg of fat mass over the 12 weeks, while those on the low-sugar diet lost an average of 2.1 kg.

No Change in Physical Activity:

Interestingly, this fat loss occurred without any changes in physical activity levels, which remained consistent throughout the study. This suggests that dietary composition alone can significantly impact fat loss, independent of exercise.

• Keto and Exercise Performance: While the keto diet shifts the body’s primary energy source from glucose to fat, this can have mixed effects on exercise performance. Some studies suggest that high-intensity, anaerobic activities may suffer due to the lack of readily available glucose. In contrast, endurance activities might benefit from the sustained energy provided by fat metabolism.
  
  

• Potential Keto Flu: Individuals starting the keto diet may experience "keto flu," a temporary set of symptoms including fatigue, headache, and irritability, as the body adapts to ketosis. This could temporarily affect energy levels and glucose handling until the body fully adjusts.

• Muscle Preservation on Keto: Despite reduced carbohydrate intake, the ketogenic diet has been found to preserve muscle mass during weight loss, likely due to the increased protein intake and the body's use of fat as an energy source rather than muscle tissue.

• Low-Sugar Diet and Long-Term Adherence: The low-sugar diet might be easier to adhere to long-term compared to the strict carbohydrate restrictions of keto. It allows for a more balanced intake of fruits, whole grains, and other carbohydrates, making it more sustainable for most people.

• Impact on Blood Lipids : While the keto diet can raise LDL cholesterol, it also tends to increase HDL (good) cholesterol, which plays a protective role against heart disease. The low-sugar diet, meanwhile, is generally associated with a balanced lipid profile, improving both LDL and HDL levels.

• Mental Clarity and Focus: Some proponents of the keto diet report improved mental clarity and focus due to the steady supply of energy from ketones, the byproducts of fat breakdown, which serve as an alternative fuel for the brain.

• Cravings and Appetite Control: The keto diet may help reduce cravings and appetite due to the satiating effects of high-fat foods and stable blood sugar levels, which can help prevent overeating and make fat loss more manageable.

Keto Diet’s Impact on Metabolism

The ketogenic diet caused significant shifts in metabolism, changing the body’s fuel preference from glucose to fats. This is a hallmark of the keto diet, where the body enters ketosis, burning fat for energy instead of carbohydrates.

Changes in Muscle Energy Use:

Participants on the keto diet showed a shift in muscle energy use, relying more on fat as fuel. While this can be beneficial for endurance in certain contexts, it raises concerns about how these adaptations might affect glucose metabolism if individuals revert to a carbohydrate-rich diet.

Long-Term Considerations and Recommendations

The study’s findings present a nuanced picture of the ketogenic diet. While effective for fat loss and certain metabolic adaptations, the keto diet also poses risks, particularly for cholesterol levels, gut health, and glucose tolerance.

Expert Recommendations:

Professor Dylan Thompson summarized, "The ketogenic diet is effective for fat loss, but it comes with varied metabolic and microbiome effects that may not suit everyone. In contrast, sugar restriction supports government guidelines for reducing free sugar intake, promoting fat loss without apparent negative health impacts."

Future Directions: The Need for Personalized Nutrition

This research underscores the importance of personalized nutrition. While some individuals may benefit from the ketogenic diet, others may face long-term health risks. Future research should focus on long-term studies to better understand how different diets affect diverse populations and to develop personalized dietary recommendations.

Funding and Support:

This research was supported by grants from The Rank Prize Funds, Cosun Nutrition Center, The University of Bath, and Ian Tarr. Additional exploratory analyses were funded by fellowships from the British Heart Foundation and Medical Research Council.

When comparing Keto vs. Low-Sugar Diets, it’s clear that both have distinct impacts on health, each with its own set of benefits and risks. The Keto diet is highly effective for fat loss and can shift the body’s metabolism to burn fat as its primary fuel source. However, it also raises significant concerns, particularly regarding increased cholesterol levels, reduced beneficial gut bacteria, and decreased glucose tolerance. These effects, if sustained over time, could lead to an elevated risk of heart disease, digestive issues, and insulin resistance.

On the other hand, the Low-Sugar diet also promotes fat loss and aligns more closely with public health guidelines, such as reducing free sugar intake to less than 5% of total energy consumption. Unlike the Keto diet, the Low-Sugar diet does not adversely affect cholesterol levels or gut health, making it a potentially safer and more sustainable option for long-term health.

In light of these findings, individuals considering a diet should weigh the potential benefits of fat loss against the long-term health implications. For those concerned about heart health, gut health, or managing glucose levels, a Low-Sugar diet may offer a balanced approach without the negative side effects associated with the Keto diet. However, for those who are able to manage the risks, particularly under medical supervision, the Keto diet could be a powerful tool for rapid fat loss.

Ultimately, the choice between Keto vs. Low-Sugar Diets should be personalized, taking into account individual health needs, goals, and risks. As research continues to evolve, it’s important to stay informed and consider consulting healthcare professionals when making significant dietary changes.