Choosing the Right Diet: An Evidence-Based Guide

Dietary advice is more accessible than ever, yet clarity has never been harder to find. At any given time, multiple dietary approaches are promoted as the solution for weight management, metabolic health, digestive symptoms or energy levels. Some are grounded in evidence and clinical application. Others are highly restrictive, poorly suited to long-term health, or beneficial only in narrow circumstances.

This blog article reviews five widely discussed dietary approaches through the lens of nutritional therapy. Each is assessed for its intended purpose, physiological impact, potential benefits and limitations. The aim is not to promote a single “best” diet, but to provide clear guidance on which approaches may be appropriate, which require caution, and why balance and individualisation remain central to effective nutrition support.

1. Carnivore Diet

What it involves

The carnivore diet consists exclusively of animal-derived foods such as meat, fish, eggs and, in some cases, dairy. All plant foods are excluded, meaning vegetables, fruits, whole grains, legumes, nuts and seeds are absent. In practice, some versions also include processed meats such as sausages and cured products.

Nutritional considerations

While animal foods provide high-quality protein, vitamin B12, iron and zinc, eliminating plant foods removes the primary dietary sources of fibre, vitamin C, folate, magnesium, potassium and a wide range of phytonutrients. Large observational and mechanistic studies consistently link fibre intake with improved gut function, reduced cardiometabolic risk and lower all-cause mortality (Slavin, 2005; Reynolds et al., 2019).

Nutrient modelling studies indicate that diets excluding plant foods struggle to meet population reference intakes for several micronutrients without supplementation, particularly vitamin C, magnesium and potassium, which play important roles in immune, cardiovascular and metabolic health (Weaver et al., 2016; Reynolds et al., 2019).

Potential benefits Very low-carbohydrate intake can suppress appetite and lead to short-term weight loss through reduced energy intake and ketosis, similar to other low-carbohydrate approaches (Hallberg et al., 2018).

Limitations There are currently no long-term randomised controlled trials assessing health outcomes on a carnivore diet. High reliance on red and processed meat is associated with increased cardiometabolic and cancer risk in large cohort studies (Micha et al., 2010; World Cancer Research Fund, 2018).

Summary The carnivore diet may lead to short-term weight loss but carries a clear risk of nutritional inadequacy due to the exclusion of plant foods and lacks robust long-term evidence.

2. Ketogenic Diet

What it involves

A ketogenic diet is characterised by very low carbohydrate intake, typically below 20–50 g per day, compared with average intakes of approximately 225–325 g per day in Western diets. Protein intake is moderate, commonly around 1.2–1.5 g per kilogram of body weight, while fat provides approximately 70–80 % of total energy intake. This macronutrient distribution induces nutritional ketosis, where ketone bodies become a primary fuel source (Bolla et al., 2019).

Evidence for benefits

Randomised trials demonstrate that ketogenic diets can improve short-term weight loss, glycaemic control and insulin sensitivity, particularly in individuals with type 2 diabetes or metabolic syndrome (Hallberg et al., 2018; Goldenberg et al., 2021). Reductions in triglycerides are commonly observed.

Limitations

Ketogenic diets are frequently lower in dietary fibre and certain micronutrients due to the exclusion of fruits, whole grains and legumes (Bolla et al., 2019). Some studies report increases in LDL cholesterol, particularly when saturated fat intake is high (Bolla et al., 2019). Long-term adherence is often challenging, and outcomes beyond one to two years remain limited.

Contextual considerations In women during perimenopause and menopause, prolonged carbohydrate restriction may increase physiological stress and negatively affect energy, sleep or hormonal balance if overall energy intake is inadequate (Mauvais-Jarvis et al., 2020).

3. Intermittent Fasting

What it involves

Intermittent fasting refers to eating patterns that alternate periods of eating and fasting. The most common format is time-restricted eating, such as 16:8, where food is consumed within an eight-hour window each day. Other approaches include the 5:2 diet and alternate-day fasting (Varady, 2022).

Why it can work

Intermittent fasting often leads to weight loss because restricting eating windows reduces total energy intake. Meta-analyses show improvements in body weight, BMI and some cardiometabolic markers comparable to continuous calorie restriction (Harris et al., 2018; Welton et al., 2020).

Strengths

• Structured approach without specific food exclusions

• May improve insulin sensitivity and triglyceride levels in some individuals

Limitations

Intermittent fasting does not inherently ensure dietary quality. Some trials show no advantage over standard calorie-restricted diets when total intake is matched (Lowe et al., 2020). Individual tolerance varies, particularly in those with blood sugar instability.

4. Mediterranean-Style Eating

What it involves

Mediterranean-style eating emphasises vegetables, fruits, whole grains, legumes, nuts, seeds, olive oil and fish, with moderate dairy intake and minimal ultra-processed foods. It is not defined by strict macronutrient targets but by food quality and dietary pattern.

Evidence base

Large randomised trials, including the PREDIMED study, demonstrate significant reductions in cardiovascular events and improvements in metabolic health compared with low-fat control diets (Estruch et al., 2013). Systematic reviews link this pattern to lower all-cause mortality and reduced risk of type 2 diabetes (Dinu et al., 2018).

Strengths

• Strongest evidence for long-term cardiometabolic health

• High fibre and phytonutrient intake supports gut health

• Sustainable and flexible

Limitations

Weight loss tends to be gradual rather than rapid, requiring consistency rather than restriction.

5. Low-FODMAP Diet

What it involves

The low-FODMAP approach is a short-term therapeutic elimination and reintroduction protocol designed to reduce fermentable carbohydrates that exacerbate symptoms in irritable bowel syndrome (IBS).

Evidence

Randomised controlled trials and systematic reviews consistently show significant reductions in IBS symptoms such as bloating and abdominal pain when compared with habitual diets (Halmos et al., 2014; Marsh et al., 2016).

Limitations

This approach is not intended for long-term use and requires careful reintroduction to maintain nutrient adequacy and gut microbiota diversity.

I Support Personalised Nutrition For Sustainable Health...

Generic diets or slimming clubs often offer a one-size-fits-all, quick-fix approach that rarely deliver lasting results.

Sustainable weight loss and improved metabolic health come from dietary and lifestyle strategies tailored to the individual, based on their blood markers, metabolism, habits and what truly works for them in life.

As a practitioner of the Metabolic Balance® programme, I help clients create personalised nutrition plans that optimise energy, balance blood sugar, and ensure nutrient adequacy for long-term wellbeing.

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References

Bolla, A. M. et al. (2019). Effects of ketogenic diets on lipid metabolism. Nutrients, 11(8), 1829.Dinu, M. et al. (2018). Mediterranean diet and health outcomes. BMJ, 361, k1075.Estruch, R. et al. (2013). Primary prevention of cardiovascular disease with a Mediterranean diet. New England Journal of Medicine, 368, 1279–1290.Goldenberg, J. Z. et al. (2021). Low-carbohydrate diets for obesity and metabolic disease. BMJ, 372, m4743.Halmos, E. P. et al. (2014). Low-FODMAP diet reduces IBS symptoms. Gastroenterology, 146(1), 67–75.Hallberg, S. J. et al. (2018). Effectiveness of ketogenic diet in type 2 diabetes. Diabetes Therapy, 9(2), 583–612.Harris, L. et al. (2018). Intermittent fasting interventions. JBI Database of Systematic Reviews.Lowe, D. A. et al. (2020). Time-restricted eating and weight loss. JAMA Internal Medicine, 180(11), 1491–1499.Marsh, A. et al. (2016). Systematic review of low-FODMAP diet. Clinical Gastroenterology and Hepatology, 14(8), 1136–1145.Mauvais-Jarvis, F. et al. (2020). Sex differences in metabolic responses to diet. Nature Reviews Endocrinology, 16, 521–538.Micha, R. et al. (2010). Red and processed meat and cardiometabolic risk. Circulation, 121, 2271–2283.Reynolds, A. et al. (2019). Carbohydrate quality and human health. The Lancet, 393, 434–445.Slavin, J. (2005). Dietary fibre and body weight. Nutrition, 21, 411–418.Varady, K. A. (2022). Intermittent fasting and metabolic health. Annual Review of Nutrition, 42, 217–235.Weaver, C. M. et al. (2016). Calcium inadequacy and health outcomes. American Journal of Clinical Nutrition, 104, 942–951.World Cancer Research Fund/AICR. (2018). Diet, Nutrition, Physical Activity and Cancer: a Global Perspective.