The 1:1 Diet — known in the Netherlands as the "1 op 1 dieet" — is one of the country's best-known commercial weight management programmes. It combines meal replacement products with weekly sessions from a personal consultant, offering the kind of structured accountability that many people find missing when dieting alone. But how does it actually work, how much does it cost, and does the science support it?
Key takeaways
- The 1:1 Diet uses a five-step programme moving from full meal replacement to normal eating
- The most restrictive phase provides around 500 to 600 calories per day and requires close supervision
- Costs typically range from €60 to €80 per week including products and consultant sessions
- Short-term results are generally good; long-term success depends heavily on behaviour change
- Independent peer-reviewed research on this specific programme is limited
- It may not be suitable for people with diabetes, kidney disease, or a history of eating disorders
How the programme is structured
The 1:1 Diet follows five steps, progressing from heavily restrictive to a normal maintenance diet as weight is lost and new habits form.
Step 1 (sole source): Only 1:1 Diet products are consumed — shakes, soups, bars, and ready meals. Calorie intake is approximately 500 to 600 kcal per day. This phase is only available with consultant supervision and is the most aggressive step.
Step 2: Four meal replacements and one conventional meal of lean protein and vegetables.
Step 3: Three meal replacements and two conventional meals.
Step 4: Two meal replacements and three conventional meals, with growing emphasis on building healthy eating habits independently.
Step 5 (maintenance): Normal diet with one optional meal replacement as a buffer. The focus shifts entirely to sustainable habits and weight management.
Consultants are independent practitioners who sell the products and provide guidance. The quality and intensity of support varies between consultants.
What the evidence says about meal replacements
Meal replacement programmes as a category have reasonable scientific support. A pooled analysis published in the International Journal of Obesity (2003) found that participants using structured meal replacement programmes lost significantly more weight over one year than those following conventional calorie-restricted diets, with the primary advantages being portion control and decision simplicity.
However, most of this research involves medically supervised or clinically structured programmes. The 1:1 Diet uses commercial consultants without medical training. For healthy adults without complicating conditions, this is generally acceptable. For people with type 2 diabetes, kidney disease, or cardiovascular conditions, medical oversight is essential before starting any very low calorie diet (VLCD).
No independent peer-reviewed trials have specifically evaluated the 1:1 Diet programme on long-term outcomes.
Strengths of the programme
The primary strength is structure. Removing food decisions entirely eliminates a major source of dietary failure for many people. The products provide consistent portioning, predictable calorie intake, and no cooking or planning requirement.
Weekly consultant contact creates accountability. Social reinforcement and regular check-ins are underappreciated drivers of behaviour change — and this programme delivers both in a consistent format.
Early results are typically visible and motivating. Seeing the scale move quickly in the first few weeks reinforces commitment, which matters for long-term adherence.
Weaknesses and risks
The cost is significant. At €60 to €80 per week, a three-to-six month programme costs between €800 and €2,000. This is out of reach for many households.
The sole source step (Step 1) is medically classified as a very low calorie diet. VLCDs carry risks including fatigue, muscle loss, electrolyte imbalances, and gallstone formation. Medical clearance before starting Step 1 is strongly advisable, particularly for anyone on medication.
The products are highly processed and artificially flavoured. Some people find this manageable; others find it a significant barrier to adherence.
The programme teaches relatively little about cooking or independent meal planning. Participants who stop using the products without having developed new eating skills are at elevated risk of regaining weight.
Who benefits most
The 1:1 Diet tends to work best for people who need external structure and regular accountability, struggle to sustain self-directed dietary plans, want visible early results as motivation to continue, and are committed to maintaining new habits after the programme ends.
It is less suitable for people with a limited budget, those with certain medical conditions, or anyone who wants to develop cooking skills and food literacy as part of their weight management.
Alternatives worth considering
If cost is a barrier but accountability appeals to you, group-based programmes through a registered dietitian are often partially reimbursed by Dutch supplementary health insurance. Self-monitoring via food tracking apps provides structure and insight at significantly lower cost.
To understand your daily calorie needs independently, see How to calculate a calorie deficit and Calorie tracking for beginners. Moveno's photo recognition lets you log meals without manual data entry — useful for the transition back to normal eating after any structured programme.
Sources
- Heymsfield SB et al. (2003). Weight management using a meal replacement strategy. International Journal of Obesity. https://doi.org/10.1038/sj.ijo.0802258
- NHS — Very low calorie diets: https://www.nhs.uk/live-well/healthy-weight/managing-your-weight/very-low-calorie-diets/
- British Dietetic Association — Meal replacement products: https://www.bda.uk.com/resource/meal-replacements.html
- Voedingscentrum — Maaltijdvervangers: https://www.voedingscentrum.nl/encyclopedie/maaltijdvervangers.aspx
