With the rising trend of personalised nutrition, many people are turning to specific diets in the hope of achieving better health, weight loss, or improved well-being. However, while certain diets may offer short-term benefits (like weight-loss), they can also have potential downsides, especially if followed longterm without professional guidance.
This article aims to provide an overview of some of the most common diets—vegetarian, vegan, low-carb high-fat (keto), paleo, carnivore, gluten-free, lactose and casein-free, glycemic load, and the Mediterranean diet—discussing their core principles, pros and cons, and potential short- and long-term nutritional deficiencies.
Before diving into these diets, it’s important to note that unless you have tested positive for a food intolerance (lactose, casein, gluten), have been diagnosed with celiac disease, or have serious food allergies (towards peanuts, seafood etc), it’s generally advisable to consume a whole foods diet that includes a wide variety of food groups: vegetables, fruits, berries, nuts, seeds, legumes, whole grains, meat, fish, and dairy. Following public dietary guidelines, such as the Estonian Food Pyramid (on below image), can serve as a good foundation for building a balanced and sustainable diet.
Photo source: Tervise Arengu Instituut
I would also like to highlight the importance of getting adequate quality calories from food (this depends on your age, body weight and lifestyle (movement, exercise and sleep). There are diets out there that advice to consume 500kcal per day for a period of time, and while this type of caloric intake can be life-saving for morbidly obese people when done once or twice, it's not something that's recommended for people to practice over and over again. Consuming fewer calories per day than your basal metabolic rate (BMR)—the number of calories your body needs to perform basic functions such as breathing, maintaining body temperature, and supporting organs function—can lead to a variety of negative health consequences. When you consistently eat below your BMR, your body may enter a state of “starvation mode,” where it slows down metabolic processes to conserve energy. This can cause a drop in energy levels, loss of muscle mass, impaired hormone production, and disruptions in thyroid function, leading to slower metabolism over time. Additionally, chronic under-eating can result in nutritional deficiencies, impacting immune function, bone health, and overall vitality. Long-term, this can increase the risk of developing conditions like osteoporosis, heart problems, or reproductive issues, especially for women. For these reasons, it’s crucial to ensure your daily caloric intake from whole foods meets at least your BMR requirements to maintain healthy bodily functions and support overall well-being.
Here are average energy daily needs based on the public dietary guidelines:
But now let's dive into different widely practiced diets.
Vegetarian Diet
A vegetarian diet excludes meat, poultry, and fish but generally includes dairy products and eggs, depending on the type of vegetarianism (lacto-ovo, lacto, or ovo vegetarian). It focuses on vegetables, fruits, whole grains, nuts, seeds, legumes, dairy, and egg-based foods.
Pros:
High in fibre, vitamins, and antioxidants from a variety of plant-based foods.
May lower the risk of chronic diseases such as cardiovascular disease, hypertension, and type 2 diabetes.
Easier to meet protein needs than a vegan diet due to the inclusion of dairy and eggs.
Can be more flexible than a vegan diet, making it easier to follow long-term.
Cons:
Potential deficiencies in vitamin B12, iron, and omega-3 fatty acids if dairy and eggs are not adequately included.
Some vegetarian diets may rely too heavily on processed meat alternatives, which can be high in sodium and preservatives.
Strict lacto or ovo vegetarian diets can lead to a lack of variety and may require careful meal planning.
Potential Nutritional Deficiencies:
Short-term: Insufficient iron and protein intake if not planned well, leading to low energy and fatigue.
Long-term: Vitamin B12 deficiency, leading to neurological issues; iron-deficiency anemia; and potential omega-3 deficiency, impacting brain and heart health.
2. Vegan Diet
A vegan diet eliminates all animal products, including meat, dairy, and eggs. It’s primarily plant-based and focuses on vegetables, fruits, whole grains, nuts, seeds, and legumes.
Pros:
High in fibre, vitamins, and antioxidants.
May reduce the risk of chronic diseases such as heart disease, hypertension, and certain cancers.
Environmentally friendly and promotes animal welfare.
Cons:
Potential deficiencies in vitamin B12, iron, omega-3 fatty acids, zinc, calcium, and protein if not carefully planned. People would typically need to supplement.
Can be challenging to obtain all essential amino acids without varied plant protein sources.
Higher risk of low bone density due to low calcium and vitamin D levels.
Potential Nutritional Deficiencies:
Short-term: Inadequate protein intake, fatigue, and anemia.
Long-term: B12 deficiency (leading to neurological problems), iron-deficiency anemia, and bone health issues.
3. Low-Carb High-Fat Diet (Keto)
The ketogenic diet emphasises low carbohydrate intake and high fat consumption to promote a state of ketosis, where the body burns fat instead of carbohydrates for fuel.
Pros:
Effective for rapid weight loss and blood sugar control.
May reduce blood pressure, triglycerides and fasting glycose.
May reduce appetite and increase satiety.
Beneficial for some neurological disorders like epilepsy.
Cons:
Difficult to maintain long-term.
Can cause nutrient deficiencies due to limited food variety.
Risk of keto flu (nausea, fatigue) and increased cholesterol levels.
Potential Nutritional Deficiencies:
Short-term: Electrolyte imbalances, dehydration, and digestive issues.
Long-term: Low intake of essential vitamins and minerals such as vitamin C, magnesium, and fibre, increasing the risk of cardiovascular disease.
4. Paleo Diet
The paleo diet is based on the presumed eating patterns of our Paleolithic ancestors, focusing on whole foods like lean meats, fish, fruits, vegetables, nuts, and seeds while avoiding grains, legumes, dairy and processed foods.
Pros:
Emphasises whole, unprocessed foods.
Rich in lean proteins and healthy fats.
May help reduce inflammation, LDL cholesterol and promote weight loss.
May help increase insulin sensitivity and improve glycose tolerance.
Cons:
Excludes entire food groups (grains, legumes, and dairy), which can result in nutrient gaps.
Can be costly and difficult to follow.
May lead to a higher intake of saturated fats depending on meat choices and the amount of meat consumed.
Potential Nutritional Deficiencies:
Short-term: Lack of energy due to lower carbohydrate intake.
Long-term: Calcium and vitamin D deficiencies, potential for low carbohydrate-related fatigue.
5. Carnivore Diet
This extreme diet includes only animal products such as meat, eggs, and dairy, excluding all plant-based foods.
Pros:
Can lead to rapid weight loss and reduced inflammation for some.
Simple to follow and eliminates common allergens.
Cons:
Extremely restrictive and lacks variety.
High in saturated fats, which may increase cardiovascular risks.
No dietary fibre, which is essential for gut health.
Can put strain on liver and kidneys
Potential Nutritional Deficiencies:
Short-term: Constipation, nutrient imbalances, and lack of phytonutrients.
Long-term: Deficiency in vitamin C, potassium, and fibre, leading to possible long-term gut health issues.
6. Gluten-Free Diet
A gluten-free diet eliminates gluten, a protein found in wheat, barley, and rye. It is essential for those with celiac disease or non-celiac gluten sensitivity.
Pros:
Essential for managing celiac disease and gluten intolerance.
May reduce bloating and digestive discomfort for sensitive individuals.
Cons:
Can lead to lower intake of essential nutrients if relying on processed gluten-free products.
Often higher in sugar and fat content.
Possible deficiencies in fibre and B vitamins.
Potential Nutritional Deficiencies:
Short-term: Lack of fibre and essential vitamins found in whole grains.
Long-term: Deficiency in iron, calcium, folate, and vitamin B12.
7. Lactose and Casein-Free Diet
Eliminates lactose (milk sugar) and casein (milk protein), usually for those who are intolerant or allergic.
Pros:
Necessary for managing lactose intolerance and dairy allergies.
Reduces digestive issues like bloating and cramps.
Cons:
Potential for calcium and vitamin D deficiencies.
Limited dairy-free alternatives may be lower in protein and nutrients.
Potential Nutritional Deficiencies:
Short-term: Lower calcium and vitamin D intake.
Long-term: Bone health issues due to chronic calcium and vitamin D deficiency.
8. Glycemic Load Diet
Focuses on consuming foods with a low glycemic load to maintain stable blood sugar levels. Glycemic load is influenced by food processing method, cooking method, by food combinations, acidity level of a food, fibre content etc.
Pros:
May help with weight management and diabetes control.
Emphasises whole, unprocessed foods.
No need to avoid but replace certain foods within food groups.
Similar to plate rule (carbohydrates, fats and protein)
Cons:
Can be complex to calculate glycemic load.
May restrict some healthy foods due to their glycemic index.
Potential Nutritional Deficiencies:
Short-term: Lower energy levels due to the exclusion of certain carbohydrates.
Long-term: Risk of inadequate carbohydrate intake, leading to fatigue and mood changes.
9. Mediterranean Diet
This diet is rich in fruits, vegetables, whole grains, legumes, nuts, and olive oil, with moderate fish, poultry and low red meat consumption; a low milk products consumption (1-2 times per week).
Pros:
High in heart-healthy fats and antioxidants.
May reduce the risk of heart disease, cancer, and cognitive decline.
Flexible and easy to maintain long-term.
Cons:
Can be expensive due to the emphasis on high-quality ingredients.
Higher fat content may not be suitable for those needing lower-fat diets.
Potential Nutritional Deficiencies:
Short-term: Few deficiencies if well-balanced.
Long-term: If improperly followed, may lead to excess caloric intake from healthy fats.
During our time at nutrition school, we had the opportunity to test several of the aforementioned diets firsthand. Our group of 25 students was divided into smaller teams, each tasked with creating menus for a specific diet, balancing them using Nutridata software, and following the diets for a duration of six days. Many of us found it challenging to adhere to the menus, as the structured approach was quite different from our usual eating habits. Additionally, with most of the diets, we observed that they could potentially lead to nutritional deficiencies, and some participants even experienced negative health effects during the trial period. Among all the diets we tried, the Mediterranean diet proved to be the most sustainable and balanced for long-term practice.
Here are couple of general guidelines, the above diets have in common and what to practice:
prefer whole foods to ultra-processed foods
reduce saturated fats and transfats in your diet
reduce added sugar and refined grains
The Bottom Line:
While each diet has its benefits and drawbacks, most of these restrictive eating patterns can lead to nutritional deficiencies or health issues if not carefully managed and practiced for a long period of time. It's important to think if the diet you are on, is serving you- are you thriving on it, is it sustainable? It's also important to not stay rigid towards one way of eating, but be open to change if your body asks for it- as our bodies changes through years and decades.
Unless medically necessary, a balanced whole foods diet that includes a variety of food groups is generally the best approach for optimal health and longevity. Using public dietary guidelines, such as for example the Estonian Food Pyramid, can provide structure and ensure a diverse intake of nutrients for long-term health and well-being.
If you are confused about different diets, have been trying various diets with no lasting success and want to know how to change your diet healthier, sustainable for your life, step by step- it might be good for you to consult with a certified nutrition counselor and health coach. Contact me at info@katrinpeo.com
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