Most of us were trained to counsel patients with obesity in a sentence: eat less, move more. Energy balance does matter, but effective obesity care requires far more than brief advice. Unstructured counselling rarely produces durable weight change because it does not account for factors that impact outcome in practice: the patient's comorbidities, treatment goals, their capacity to sustain change, and variability in metabolic response.
Over the past decade, several landmark trials have shown that structured lifestyle intervention can produce clinically meaningful weight loss. The benefits of weight loss often increase with the amount of weight lost, that no single macronutrient distribution is superior on average, and that individual response to the same foods can vary. [1–4] This article draws on that evidence, alongside current guidance, to outline an individualised approach to nutrition and physical activity in adults with obesity.
Why generic advice falls short
The strongest evidence that lifestyle therapy can work comes from programmes that look nothing like a single consultation. In the Look AHEAD trial, 5,145 adults with type 2 diabetes and overweight or obesity received either diabetes support and education or an intensive lifestyle intervention combining calorie restriction (1,200–1,800 kcal/day), partial meal replacement, at least 175 minutes per week of moderate-intensity activity and frequent group and individual sessions. The intensive arm lost 8.6% of body weight at one year compared with 0.7% in controls, and maintained a smaller difference (6.0% vs 3.5%) at the end of the intervention. [3] The DiRECT trial used an even more structured model in UK primary care, with total diet replacement followed by stepped food reintroduction and long-term maintenance support delivered by practice nurses and dietitians [2].
What these programmes share is a structure: clear targets, self-monitoring, regular contact and a planned approach to maintenance. Weight regain is a common physiological response to energy restriction rather than a failure of willpower, and ongoing support can help limit it. Maintenance should therefore be planned from the outset. For the clinician, referral to a structured service, or building that structure into follow-up, is likely to be more effective than repeated advice alone.
How much weight loss, and for what?
The weight loss target is guided by clinical goals.. Modest loss of around 5% can improve glycaemia, blood pressure and lipids, and in Look AHEAD the intensive intervention was accompanied by improvements in glycated haemoglobin (HbA1c), fitness and physical function [3]. However, the trial was stopped for futility after a median follow-up of 9.6 years, having shown no reduction in its primary cardiovascular outcome (hazard ratio 0.95, 95% CI 0.83–1.09). The narrowing weight difference between arms and greater use of cardioprotective medication in the control group were possible contributors, although they do not establish why the result was neutral.
DiRECT examined the effect of greater weight loss in 306 adults with type 2 diabetes diagnosed within the previous six years who were not using insulin. At 12 months, mean weight loss was 10.0 kg in the intervention group and 1.0 kg in controls, and 46% of intervention participants were in remission compared with 4% of controls. Remission rates rose with greater weight loss: 7% among those who maintained less than 5 kg, 34% among those losing 5–10 kg, 57% among those losing 10–15 kg and 86% among those losing 15 kg or more. [2]
For selected adults with relatively recent type 2 diabetes, substantial weight loss can therefore increase the likelihood of remission. Because DiRECT studied a defined population, these findings support individualised targets that take account of starting weight, diabetes duration, treatment suitability and clinical circumstances, rather than a single threshold for all patients. [2]
Other conditions have their own evidence base. For metabolic dysfunction-associated steatotic liver disease (MASLD), the target should reflect disease severity: sustained weight loss of at least 5% can reduce liver fat, 7–10% may improve liver inflammation, and 10% or more may be needed to improve fibrosis [5]. In obstructive sleep apnoea (OSA), weight management is recommended, but the degree of loss required and the clinical response vary, so it should be individualised and integrated with appropriate OSA treatment [6].
Choosing the diet
Once a target is agreed, the question becomes which diet to use. Public debate often focusses on low-fat versus low carbohydrate, with claims that genetics or insulin response should guide choices. The DIETFITS trial tested these claims in 609 adults without diabetes, randomised to a healthy low-fat or healthy low-carbohydrate diet for 12 months. Both groups were coached to eat whole foods, cook at home and limit added sugar, refined grains and highly processed products, without explicit calorie targets. Mean weight change was −5.3 kg and −6.0 kg respectively, with no statistically significant difference, and neither the genotype pattern nor baseline insulin secretion predicted differential weight loss. This indicates that neither diets could establish superiority. [1]
In practice, this supports offering a choice among evidence-based, high-quality dietary patterns and allowing preference, cultural food habits, cost, cooking skills and comorbidity to inform it. A lower-carbohydrate pattern may suit a patient with diabetes who finds it easier to sustain; a Mediterranean-style or lower saturated fat pattern may be preferable where low-density lipoprotein (LDL) cholesterol is the main concern. Current evidence does not support genetic testing to select a weight-loss diet.
Physical activity: beyond burning calories
Exercise alone usually produces modest weight loss, which can lead patients and clinicians to undervalue it. In Look AHEAD, physical activity was a core component of the intervention, which improved fitness, mobility and glycaemic control. [3] Activity is also associated with better weight maintenance after loss, and it benefits insulin sensitivity, mood and cardiorespiratory fitness independently of weight change.
World Health Organization (WHO) guidance for adults recommends 150–300 minutes per week of moderate-intensity aerobic activity, or an equivalent amount of vigorous activity, plus muscle-strengthening activity on two or more days. [8] This is a general adult target and should be adapted to clinical status, functional ability, contraindications and baseline fitness, with a gradual build-up for patients who are currently inactive.
Resistance training also deserves emphasis because substantial weight loss can include loss of lean mass. The STEP 1 trial with semaglutide showed that lean tissue made up a meaningful proportion of the weight lost [7]. The magnitude varies by intervention, population and measurement method. Adequate protein intake and strength training are reasonable measures to help preserve muscle, particularly in older adults.
Individual variation and precision nutrition
The heterogeneity seen in DIETFITS may partly reflect biological differences between individuals. [1] Zeevi and colleagues monitored glucose continuously in 800 adults, capturing responses to 46,898 meals. [4] They found considerable interpersonal variation in the post-meal glucose increase with the same foods. By combining meal content with data on each participant's gut microbiome, blood tests, body measurements and daily habits, the investigators developed a machine-learning model that forecast these responses more accurately than carbohydrate counting alone and confirmed its performance in a second cohort. A small, randomised crossover study then showed that diets built from the model's predictions reduced post-meal glucose. These findings need cautious interpretation. The outcomes were short-term glycaemic responses rather than weight, long-term HbA1c or clinical events, and the study population was largely metabolically healthy. The work helps explain why uniform dietary rules suit some patients better than others. In selected patients, such as those with diabetes in whom glycaemic control is a priority, CGM-informed food choices may become a useful adjunct to established dietary approaches.
A practical approach
Bringing this evidence together suggests a sequence for individualised management:
1. Assess and agree the goal. Identify complications and the patient's priorities, then set an individualised weight target informed by the relevant evidence. [2,3,5,6]
2. Choose a sustainable dietary pattern. Prioritise diet quality and let preference and comorbidity guide macronutrient emphasis]; consider a structured low-energy diet for selected patients in whom substantial weight loss is the goal. [1,2]
3. Prescribe physical activity for broader health benefits. Combine aerobic and muscle-strengthening activity, adapted to the individual. [3,8]
4. Protect lean mass during substantial weight loss. Encourage resistance training and adequate protein intake, particularly with intensive dietary or pharmacological treatment.[7]
5. Plan maintenance. Build in regular review and early action on weight regain [2,3].
6. Use newer tools selectively. Consider CGM-informed advice only where glycaemic control is a priority [4].
Conclusion
The evidence supports a shift from generic advice to individualised, goal-directed management. Structured lifestyle intervention can produce clinically meaningful weight loss, the likelihood of some outcomes increases with greater loss, no single macronutrient distribution is superior on average and metabolic responses to food vary more than standard advice assumes. Nutrition and physical activity are foundational to obesity care but they form one part of comprehensive management alongside anti-obesity medication or metabolic surgery where indicated.