Is it a plateau, or just a noisy few weeks?

First, is it a plateau?

Two or three flat weeks are often not a plateau yet. Over two weeks of ordinary life, Bhutani and colleagues found 84% of the change in body weight was fat-free mass rather than fat (Physiological Reports, 2017). A couple of flat weeks can hide a real change in fat or simply reflect water. The longer explanation is in why weight fluctuates day to day.

The first useful question is therefore not why the loss stopped, but whether a trend across several weeks has actually leveled off.

Why does weight loss slow down at the same intake?

At a fixed intake, weight loss is expected to slow and eventually stop. A smaller body uses less energy, so an intake that was a deficit at the start becomes a smaller one. Hall and colleagues’ model in The Lancet (2011) shows weight settling at a new level over several years, with about half of the change in the first year. Anything that promised a straight line was using the 3,500-calorie rule.

In practice the plateau often arrives sooner. In The American Journal of Clinical Nutrition (2014), Thomas and colleagues note that clinical weight loss typically stabilizes at about six months. Validated energy-balance models put the plateau at one to two years. Adding metabolic adaptation to their model raised the final weight but did not move the timing.

A model with intermittent lapses in diet adherence did move the timing. Thomas and colleagues also showed that a six-month plateau can occur even with what they describe as high adherence.

What can cause a weight-loss plateau?

Five explanations come up most often: lower expenditure, higher appetite, intake that drifts, water, and medications or health conditions. The list does not identify your cause. Several can happen at once, and none can be confirmed from a weight trend alone.

• 1You use less energy at a lower weightExpenditure

  In The New England Journal of Medicine (1995), holding weight 10% or more below usual lowered total energy expenditure by about 6 to 8 calories per kilogram of fat-free mass per day. That is more than the change in body size alone would explain. Six months of calorie restriction in PLOS ONE (2009) lowered expenditure adjusted for body composition by about 431 calories a day at three months and 240 at six. Physical activity fell too.

• 2Appetite rises as weight fallsIntake

  Analyzing a 52-week trial of 153 people, Obesity (2016) estimated that eating rose by about 100 calories a day for each kilogram lost. That rise is more than three times the fall in expenditure. Hall and Kahan summarize the pair in Medical Clinics of North America (2018): about 20 to 30 calories a day less expenditure and about 100 more appetite per kilogram lost. These are model-based estimates, not direct measurements of hunger.

• 3Intake has drifted without being noticedRecords

  Estimating intake is hard. Pooling five large US validation studies, American Journal of Epidemiology (2014) found energy intake under-reported by about 28% on a food frequency questionnaire and 15% on a single 24-hour recall. Body mass index, education and age were linked to how much. In the clinic data Hall and colleagues modeled, the weight curve implied that an initial 800-calorie daily cut had been “rapidly and progressively relaxed.” The finding describes those patients’ curve, not anyone else’s.

• 4Water is hiding a change in fatComposition

  Scale weight and body fat can move differently. In Cell Metabolism (2015), 19 adults in a metabolic ward ate the same calories on two diets for six days each. They lost 1.85 kg of body weight on carbohydrate restriction and 1.3 kg on fat restriction. Yet by direct balance measurement they lost less body fat on the carbohydrate-restricted diet. Reviewing the evidence in Advances in Nutrition (2017), Cava and colleagues report that fat-free mass makes up about 20 to 30% of weight lost in people with overweight or obesity.

• 5A medication or health conditionHealth

  The National Institute of Diabetes and Digestive and Kidney Diseases lists medicines that may contribute to weight gain. The list includes some used for epilepsy, depression or psychotic disorders, corticosteroids, insulin and sulfonylureas, some blood pressure medicines and some antihistamines. It also names health problems including polycystic ovary syndrome, Cushing’s syndrome and hypothyroidism (NIDDK). Never stop or change a medication on your own; ask the prescriber.

How does a longer trend help with a plateau?

A longer trend makes some explanations more or less likely, without diagnosing anything.

• If the trend is flat and your logged intake looks unchanged, both a lower expenditure and a gap between what is logged and what is eaten remain possible. A couple of weeks of especially consistent logging, including weighing portions, can show whether the record matches what you thought you were eating.
• If the scale is flat but measurements, photos or training loads are changing, body composition may be shifting under a stable weight.
• If weight changes sharply without a change in habits, or with other symptoms, contact a clinician rather than adjusting a target.

What to change, if anything, and by how much, belongs to a conversation with a doctor or registered dietitian who knows your health. A larger cut is not automatically the answer. Appetite rises and lean tissue is lost as weight falls, which is part of why the question is worth discussing rather than guessing.

What plateau research can and cannot tell you