​Take-home messages🔑: 

Introduction🍽️

We derive energy from foods containing carbohydrates, proteins and fats, collectively known as macronutrients. The primary principle for achieving weight loss is to consume less energy than is expended, creating an energy deficit that prompts the body to utilise its fat stores. This is why weight loss can occur on any diet that restricts portion sizes, specific foods or overall energy intake, whether it be low-carbohydrate, low-fat or balanced (1), as well as through exercise programmes that burn energy, with or without dietary restrictions. Diets that exclude particular foods or entire food groups or emphasise single foods, can be challenging to maintain long-term due to their lack of flexibility. Most diets reduce access to energy-dense, highly palatable foods, which aids in weight loss. While any diet that restricts energy intake can lead to weight loss, it is essential to consider the associated disease risks, whether the diet meets nutritional needs and its sustainability for long-term success. Adherence to restrictive diets is often low outside of controlled research settings, affecting their real-world effectiveness. The set point theory suggests that the body has a natural weight range, or "set point," that it tends to maintain, making it difficult to sustain weight loss or gain outside of this range. This is why maintaining weight loss can be challenging, and the more drastically a diet is altered to achieve weight loss, the easier it may be to regain weight once the diet is stopped.

In the nutrition community, low-carbohydrate diets—which limit carbohydrate intake in favour of increased protein, fat or both (such as Atkins or Keto diets)—along with low-fat and balanced diets, are widely debated due to their potential impact on health and disease (2). Normally, the body uses glucose (derived from carbohydrates) as its primary energy source. However, when carbohydrates are restricted, the body shifts to using fatty acids and ketones for fuel (3). This metabolic state, known as ketosis, occurs because the lack of glucose forces the body to break down stored fat into fatty acids, which are then converted into ketones for energy. This shift is one reason why low-carbohydrate diets are heavily debated in terms of their long-term health effects.

Here, I present evidence supporting the effectiveness of low-carbohydrate diets for weight loss, while also discussing the potential health consequences that dieters should consider.

Effectiveness of Low-Carbohydrate Diets on Weight Loss: Evidence from Studies Summarising Weight Loss Trials🏋️‍♀️

When interpreting results from low-carbohydrate diets (Keto) diet trials one must consider the significant water weight loss due to glycogen depletion, which can affect body weight results and that must be properly accounted for. In their meta-analysis Nordmann and other researchers (4) compared the effects of low-carbohydrate diets followed for 6 months without energy restriction versus energy-restricted low-fat diets on weight loss. They concluded that low-carbohydrate, non–energy-restricted diets are at least as effective as low-fat, energy-restricted diets in inducing weight loss.

Similarly, Bueno et al. (5) summarised 13 studies that compared the long-term effects of very-low-carbohydrate ketogenic diets (with no more than 50 g of carbohydrates per day) and low-fat diets. Their findings showed that individuals on very-low-carbohydrate ketogenic diets experienced greater weight loss than those on low-fat diets.

In another meta-analysis (6) low-carbohydrate diets, were shown to be effective for weight loss, with significant reductions in body weight at both 6-month (8.73 kg) and 12-month (7.25 kg) follow-ups. However, the differences in weight loss between low-carbohydrate and low-fat diets were minimal, reinforcing the idea that adherence to the chosen diet plays a more crucial role in achieving weight loss than the specific macronutrient composition. Similarly, Naude and colleagues (7) summarised 19 good quality randomised controlled trails and concluded that weight loss could be achieved irrespective of whether the diet is low in carbohydrates or balanced.

Overall, the evidence suggests that low-carbohydrate, low-fat and balanced diets are all effective in reducing weight, with adherence being the key factor in long-term success.

Tailoring Diets Based on Insulin Sensitivity and Genetics: Personalised Weight Loss Strategies 🧬

The table below summarises findings from various studies on the relationship between diet, insulin sensitivity and genetics. The key takeaway is that insulin sensitivity and genetic factors i.e. the IRS1 genotype can influence how effective certain diets are for weight loss and insulin resistance improvement. Tailoring diets based on these factors may lead to better outcomes, particularly with low-carbohydrate diets being more beneficial for insulin-resistant individuals. However, in some cases (8), genetics and insulin secretion were found to have no significant effect on weight loss between different diets.

Table: Summary of Studies on Diet, Insulin Sensitivity and Genetic Factors

Health Implications of Low-Carbohydrate Diets❤️

When selecting a weight loss strategy, it is crucial to consider not only the immediate effects on body weight but also the broader health impacts. Different diets, particularly those with low-carbohydrate approaches, can influence various aspects of health, including cardiovascular risk factors, metabolic health and even long-term mortality. Therefore, dieters must balance weight loss goals with the potential long-term health consequences of their chosen dietary approach.

Cholesterol Changes and Cardiovascular Health

There are health aspects to consider when choosing a weight loss strategy. Nordmann and colleagues (4) warned against the unfavourable changes in low-density lipoprotein cholesterol (the bad cholesterol) values when consuming a low-carbohydrate diets to induce weight loss. Bueno et al. (5) found that the very low carbohydrate diet decreased triglycerides (triacylglycerol) and diastolic blood pressure, but increased both the good (high-density lipoprotein, HDL) and bad (low-density lipoprotein, LDL) cholesterol.

Animal vs. Plant Protein in Low-Carbohydrate Diets

Song et al. (14) showed that high animal protein intake was positively associated with cardiovascular mortality and high plant protein intake was inversely with all-cause and cardiovascular mortality. Therefore, dieters considering following a high protein diet could substitute animal protein especially that from processed meat and red meat with plant protein because they are linked to increased cancer, cardiovascular and type 2 diabetes risk (15-17).

Low-Carbohydrate Diets: Metabolic Health and Type 2 Diabetes Risk

Recent evidence presents a nuanced view of low-carbohydrate diets in relation to metabolic health and type 2 diabetes. A large Australian cohort study found that a higher low-carbohydrate diet score was associated with an increased risk of developing type 2 diabetes, primarily mediated by obesity—suggesting that low-carbohydrate diets may elevate diabetes risk, particularly in individuals predisposed to excess weight (18). A weight-maintaining ketogenic diet, even with increased ketone levels, did not improve glucose tolerance, insulin sensitivity or other metabolic parameters in obese individuals with type 2 diabetes (19).

In contrast, a systematic review and meta-analysis of 41 randomised controlled trials assessed the effects of low-carbohydrate diets interventions in adults with metabolic syndrome. The findings demonstrated significant improvements in key metabolic biomarkers, including body mass index (BMI), waist circumference, blood pressure, glycated haemoglobin (HbA1c), triglycerides and high-density lipoprotein cholesterol (20). These results indicate potential benefits of low-carbohydrate diets for managing metabolic syndrome, though further research is needed to determine optimal carbohydrate thresholds and intervention duration.

Mortality Risk and Macronutrient Balance

In a summary of observational studies low-carbohydrate diets were associated with a higher risk of all-cause mortality but not with cardiovascular mortality (21). Likewise, Seidelmann et al. (22) found that both high and low percentages of carbohydrate diets were associated with increased mortality, with minimal risk observed at 50–55% of total energy provided by carbohydrates. Similar to Noto and colleagues, Seidelmann et al. (22) observed that low carbohydrate dietary patterns favouring animal-derived protein and fat sources (lamb, beef, pork and chicken), were associated with higher mortality, whereas those that favoured plant-derived protein and fat intake (from sources such as vegetables, nuts, peanut butter and whole-grain breads) were associated with lower mortality.

Cognitive Effects of Very Low-Carbohydrate Diets

Furthermore, a study by Wing et al. (23) showed that a very low carbohydrate ketogenic diet reduced weight, but worsened higher order mental processing and flexibility impairing problem solving. A large prospective cohort study examined the relationship between long-term red meat intake and cognitive outcomes in 133,771 participants (24). Higher consumption of processed red meat (≥0.25 servings/day) was linked to a 13% increased risk of dementia and 14% higher risk of subjective cognitive decline (24). Additionally, processed red meat intake was associated with accelerated cognitive aging, particularly in global cognition and verbal memory. Higher unprocessed red meat intake (≥1 serving/day) was also linked to a 16% higher risk of subjective cognitive decline (24). Notably, replacing one daily serving of processed red meat with nuts and legumes was associated with a 19% lower risk of dementia and 21% lower risk of subjective cognitive decline (24). This has important implications for individuals following a low-carbohydrate diet for weight loss, as such diets often emphasise protein sources, including red meat.

Kidney Health

A cohort study of 1,797 Tehranian adults found that a low-carbohydrate, high-protein (LCHP) diet score was associated with an increased risk of chronic kidney disease over 6.1 years—independent of major risk factors (25). A systematic review and meta-analysis of 30 studies (n = 2,160) reported that high-protein diets increased glomerular filtration rate, serum urea, urinary calcium and uric acid levels compared to normal/low-protein diets, raising concerns about renal strain, particularly in obese individuals consuming high levels of animal protein (26).

In contrast, a meta-analysis of nine randomised controlled trials involving 1,687 overweight and obese individuals without chronic kidney disease found that low-carbohydrate diets led to a greater increase in estimated glomerular filtration rate than control diets, suggesting no adverse impact on renal function in this population (27). Similarly, a one-year randomised controlled trial in 68 adults with abdominal obesity showed no significant differences in serum creatinine, estimated glomerular filtration rate or urinary albumin excretion between very-low-carbohydrate and high-carbohydrate diets, indicating that long-term low-carbohydrate diets are safe for individuals with normal kidney function (28).

In summary, while high-protein diets may pose risks for kidney health—especially in vulnerable groups—low-carbohydrate diets appear safe and potentially beneficial for renal function in individuals without pre-existing kidney disease.

Importance of Macronutrient Quality

It is not just the quantity (% contribution to total energy intake) but also the quality (type and nature) of macronutrients such as carbohydrates that are critical in weight loss diets (7) and these profoundly affects health outcomes of dieters. Substituting refined carbohydrates, such as sugary snacks and white bread, with high-quality alternatives—such as whole grains, legumes, fruits and vegetables, which provide more fibre, nutrients and slow-releasing energy—is always a smart strategy. Similarly, replacing unhealthy fats, such as trans fats and excessive saturated fats found in processed foods, with healthy fats from sources such as nuts, seeds, avocados and olive oil, can s enhance cardiovascular health and overall well-being.

Binge Eating after Low-carbohydrate Diet

Adherence to an unsupervised low-carbohydrate diet among Brazilian university students was associated with worsening binge eating and heightened food cravings over a three-month period, particularly when culturally significant foods such as rice were restricted (29).

Conclusion📝

While low-carbohydrate diets have demonstrated effectiveness in promoting weight loss, particularly in the short term, their long-term health implications and sustainability remain debated. Evidence supports that weight loss can be achieved with various dietary approaches—whether low-carbohydrate, low-fat, or balanced—provided there is adherence to the chosen regimen. However, individual factors such as insulin sensitivity and genetics can influence the effectiveness of these diets, particularly for insulin-resistant individuals who may benefit more from low-carbohydrate approaches.

Importantly, beyond weight loss, the quality of macronutrients plays a critical role in determining long-term health outcomes. Substituting refined carbohydrates with nutrient-dense, high-fibre alternatives and replacing unhealthy fats with healthier options can contribute to better cardiovascular health and overall well-being.

For those without insulin resistance, a balanced diet that meets the body’s micronutrient needs—providing 50–55% of total energy from high-quality carbohydrates (complex carbohydrates with low glycaemic indexes), protein primarily from plant sources and healthy fats such as mono-unsaturated fatty acids (MUFAs) and poly-unsaturated fatty acids (PUFAs)—appears to be the most effective for long-term health. Adopting balanced dietary changes and increasing physical activity levels are recommended both for achieving weight loss and for keeping the weight off long-term (30).

Reflection Exercises🤔

·         Reflect on your current diet. How much of it is composed of carbohydrates, proteins and fats?

·         Consider your own or someone else's weight loss journey. Were specific diets such as low-carbohydrate or low-fat used? Reflect on how successful these diets were in terms of both weight loss and long-term maintenance.

·         Reflect on how much you know about the importance of macronutrients. How has your understanding of carbohydrates, proteins and fats changed after reading about their role in both weight loss and overall health?

·         Reflect on the association between high animal protein intake and cancer and cardiovascular risks. How could substituting plant-based proteins in your diet impact your long-term health?

·         Reflect on how a very low-carbohydrate diet could affect cognitive functions, such as problem-solving and flexibility. Have you ever noticed a change in mental performance when following a specific diet?

·         Reflect on the idea of balance in a diet. How do you currently balance your carbohydrate, protein and fat intake? What changes could you make to ensure you are meeting your micronutrient requirements?

·         Consider the challenges of maintaining weight loss after dieting. Have you or someone you know experienced weight regain after a restrictive diet? Reflect on why balanced diets may be more sustainable.

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References 📝

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Always seek guidance from dietitians for personalised diets and weight management plans.

In developing this work, the author
utilised ChatGPT-4 to assist with language editing, not for content generation.