The ketogenic (keto) and Mediterranean diets have both gained significant popularity in recent years, particularly for their potential benefits in weight loss, heart health, and blood sugar management. However, consensus has not been reached on what constitutes an optimal diet in individuals with prediabetes and type 2 diabetes mellitus (T2DM). In 2018-2019, both Diabetes UK and the American Diabetes Association (ADA) released nutrition guidelines for preventing and managing diabetes (1, 2), endorsing an individualized approach and agreeing on several key nutrition recommendations, including: 1) incorporating nonstarchy vegetables; and 2) minimizing added sugars and refined grains. This article aims to provide a comprehensive comparison of these two dietary approaches, examining their key characteristics, benefits, drawbacks, and sustainability.
Key Characteristics
Ketogenic Diet
The ketogenic diet is characterized by a very low carbohydrate, high-fat intake. A typical macronutrient distribution range for the keto diet is 70-75% calories from fat, 20-25% calories from protein, and 5% calories from carbs. This drastic reduction in carbohydrate intake forces the body to enter a metabolic state called ketosis, where it begins to use fat for fuel instead of glucose. During the WFKD phase, participants were counseled to sustain nutritional ketosis by limiting carbohydrates to 20-50 g/day and keeping proteins to ∼1.5 g/kg ideal body weight/day, with the remaining kcals coming from fats. This meant they were to exclude legumes, most fruits (limited amounts of some berries were allowed), all grains, and all sugars. The keto diet was originally used as a short-term therapeutic option for poorly controlled seizures. In recent years, the keto diet has become a popular weight loss strategy.
Mediterranean Diet
The traditional Mediterranean diet is rich in plant foods (nuts, beans, legumes, whole grains), fish, poultry, limited red meat, unsaturated vegetable oils, and, in moderation, red wine. During the Med-Plus phase, participants were encouraged to sustain a Mediterranean diet based on recommendations from the Mediterranean Diet Pyramid (19), with the additional restriction of avoiding added sugars and refined grains (hence, the referral to this as the Med-Plus). The macronutrient composition of the Mediterranean diet generally is 45% to 55% of calories from high-quality carbs, 25% to 35% of calories from fat, and 15% to 20% of calories from lean proteins. In both dietary phases, whole foods were promoted and all processed foods and added sugars were strongly discouraged (Figure 1B).
Benefits of Each Diet
Ketogenic Diet
The keto diet has been highlighted for its ability to jump-start weight loss, enhance mental clarity, and boost energy levels. Some articles suggest that keto can improve glycemic control and reduce heart disease risk. The ketogenic diet has also been studied for its ability to enhance brain health. In fact, the ketone bodies that are produced as an alternative source of energy on the keto diet may have neuroprotective properties and are even being studied for their ability to protect against conditions like Alzheimer’s disease (23). What’s more, the ketogenic diet is also often used as a treatment for epilepsy. According to one review, several variations of the keto diet have been used to prevent seizures since the 1920s and are considered an effective treatment for people who have epilepsy that doesn’t respond to medications (24).
Mediterranean Diet
Numerous studies link the Mediterranean diet to better brain health and lower risk of neurological problems. The high antioxidant and healthy fat content have been linked to better memory, improved brain plasticity, and a decreased risk of neurodegenerative diseases such as Alzheimer’s. Research suggests that the Mediterranean diet may help reduce inflammation and oxidative stress in the brain. Studies also show that the Mediterranean diet could help decrease blood pressure levels and protect against plaque buildup in the arteries, both of which can contribute to heart disease (5, 6). Research shows that the Mediterranean diet can improve blood sugar management and may be associated with a lower risk of developing type 2 diabetes (15, 16).
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Drawbacks of Each Diet
Ketogenic Diet
There are limited studies on the impact on health for those following the keto diet long-term. However, other articles suggest the keto diet has poor long-term adherence and can have long-term health consequences. The restrictive nature of the keto diet can lead to nutrient deficiencies, whereas the Mediterranean diet is rich in nutrient-dense, whole foods that provide more essential nutrients. While some studies have suggested the ketogenic diet can improve heart health due to the high-fat nature of the diet, the keto diet may actually increase LDL levels over time if the right types of fats aren’t being consumed. Additionally, the rapid weight loss nature of the keto diet may be difficult to sustain. The keto diet is more polarizing," he said.
The keto diet is much more restrictive than the Mediterranean diet and may be more difficult to follow, as it requires you to track your carb intake carefully. Not only can tracking be stressful and time-consuming, but some research suggests that food logging could foster an unhealthy relationship with food and cause feelings of guilt, shame, anxiety, or inadequacy after eating (27, 28). The keto diet can also cause several side effects initially as your body adjusts, known as the “keto flu.” Some of the most commonly reported side effects associated with the ketogenic diet include headache, nausea, fatigue, dizziness, and brain fog (29). Though there are limited studies on the long-term safety or side effects of the ketogenic diet, some research suggests that it could increase your risk of fatty liver disease, constipation, and kidney stones (2). Furthermore, careful planning is needed to ensure nutrient needs are met on the ketogenic diet, as it may also be linked to a higher risk of vitamin and mineral deficiencies (30). Restrictive weight loss diets, including the keto diet, may also have negative effects on mental health and body image. In fact, they could even contribute to disordered eating behaviors, including feeling fixated on food, ignoring feelings of hunger and satiety (fullness), and developing an unhealthy obsession with healthy eating (31).
Mediterranean Diet
Unlike many other diet plans, the Mediterranean diet doesn’t have any strict rules or regulations to follow. While some people may enjoy the flexibility that this eating pattern offers, others may prefer structured diets that provide more detailed guidance. Although red wine has been linked to several health benefits, some people may need to limit their alcohol intake, including those who are pregnant or have a history of alcohol use disorder (25, 26). Plus, because the Mediterranean diet promotes mostly whole and minimally-processed foods, it can be more expensive and time-consuming to follow than some other plans as well, which might be a key consideration for some.
Keto-Med Study: A Direct Comparison
The Keto-Med study was a single-site, randomized, crossover clinical trial comparing 2 metabolically distinct diets-the WFKD compared with the Med-Plus-among individuals with prediabetes and T2DM. The primary outcome was the percentage change in HbA1c from baseline after 12 weeks on each diet; secondary outcomes included fasting insulin and blood lipid values. Forty participants aged ≥18 years with prediabetes or T2DM followed the well-formulated ketogenic diet (WFKD) and the Mediterranean-plus diet (Med-Plus) for 12 weeks each, in random order. The diets shared the 3 key similarities noted above. The Med-Plus incorporated legumes, fruits, and whole, intact grains, while the WFKD avoided them.
Results
The HbA1c values did not differ between diets at 12 weeks. Triglycerides decreased more for the WFKD [percentage changes, −16% (SEM, 4%) compared with −5% (SEM, 6%) for the Med-Plus; P = 0.02] and LDL cholesterol was higher for the WFKD [percentage changes, +10% (SEM, 4%) compared with −5% (SEM, 5%) for the Med-Plus; P = 0.01]. Weight decreased 8% (SEM, 1%) compared with 7% (SEM, 1%) and HDL cholesterol increased 11% (SEM, 2%) compared with 7% (SEM, 3%) for the WFKD compared with the Med-Plus, respectively; however, there was a significant interaction of diet × order for both. Participants had lower intakes of fiber and 3 nutrients on the WFKD compared with the Med-Plus. HbA1c values were not different between diet phases after 12 weeks, but improved from baseline on both diets, likely due to several shared dietary aspects. The WFKD led to a greater decrease in triglycerides, but also had potential untoward risks from elevated LDL cholesterol and lower nutrient intakes from avoiding legumes, fruits, and whole, intact grains, as well as being less sustainable.
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Long-Term Sustainability and Adherence
Due to its restrictive nature, the keto diet is intended for short-term use. In the long run, a restrictive diet can lead to nutritional deficiencies. The Mediterranean diet has many health benefits. It is more flexible and, therefore, more nutritionally sustainable. Additionally, at 12 weeks, participants were more likely to adhere to the Mediterranean diet than the keto diet, suggesting that the Mediterranean diet is more sustainable. The researchers noted that the rise in LDL cholesterol, decrease in fiber intake and nutrient deficiencies associated with the keto diet are “concerning,” but longer-term studies are needed to fully understand the clinical implications.
When the research team checked in with the participants three months after the trial, on average, they had maintained lower blood glucose levels and weight loss. Notably, they were eating closer to a Mediterranean diet than to a keto diet.
Transitioning from Keto to Mediterranean
Transitioning from the keto diet to the Mediterranean diet offers a sustainable and nutritionally balanced diet approach to long-term health and weight loss, if desired. The keto diet is a low-carb, high-fat regimen that induces ketosis, but its restrictive nature makes it challenging to maintain and may lead to nutrient deficiencies. In contrast, the Mediterranean diet emphasizes a balanced intake of healthy fats, vegetables such as leafy greens, quality carbohydrates, and nutrient-dense foods.
Start by gradually increasing your intake of complex carbohydrates by 10-20g toward your goal amount. The ketogenic diet includes minimal carbohydrates, which your body has become accustomed to. The keto diet only contains 5-10%. Comparatively, the Mediterranean diet consists of an average of 45-55% calories from high-quality carbs. Reintroducing carbs into the diet can lead to water-weight gain, in which the body stores glycogen in the muscles and liver. Glycogen retains water, and so transitioning from the keto diet to a Mediterranean diet can lead to an increase in water weight.
The keto diet prioritizes fat quantity, which allows more saturated fat from animal products and coconut oil. The Mediterranean diet emphasizes fat quality, including heart-healthy monounsaturated fats from olive oil and omega-3-rich polyunsaturated fats from fish and nuts. If you have been following a high-fat diet such as the keto diet, it may be wise to check your lipid panels to ensure your cholesterol has not risen. When transitioning off of a limited diet like the low-carb limits of the keto diet, it may be tempting to overeat foods that were previously restricted. However, it’s important to increase the amount of carbs you eat gradually to avoid excess weight gain. Remember, the Mediterranean diet is about 45-55% calories from carbs.
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Impact on Athletic Performance
Regardless of whether you’re following a Keto diet or a Mediterranean diet, exercise remains beneficial. You may find your athletic performance boosts on a Mediterranean diet. Carbohydrate intake before a workout is essential. Complex carbohydrates help maintain blood sugar levels and prevent fatigue during intense or prolonged exercise. Although the Mediterranean diet is higher in carbs than the Keto diet, the Mediterranean diet is not considered a high-carbohydrate diet. The Mediterranean diet typically includes about 45-55% of calories from carbohydrates, which is moderate in comparison to other popular high-carb diets.
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