The study is fine, but seems to show something else entirely by design and results. The 14 pairs of twin cows lost a somewhat significant amount of weight on a very low calorie diet plus exercise: an average of 17.6 lbs in 4 weeks. http://www.nature.com/ijo/journal/v25/n4/full/0801559a.html https://www.andeal.org/worksheet.cfm?worksheet_id=252857 Data Collection Summary: Timing of Measurements:  Body composition and RMR were assessed before and after weight loss. Dependent Variables Body composition assessed by body weight, BMI, hydrostatic weighing RMR assessed by indirect calorimetry Independent Variables VLCD Programmed exercise ( a 4 km walk, 20 minutes on a stationary bicycle at 60% VO2max, 30 minutes of aerobic exercises) Control Variables Daily determination of urinary ketones to assess diet adherence Daily pedometer measurements to assess compliance to exercise Description of Actual Data Sample: Initial N: 14 pairs of female obese identical twins Attrition (final N): 14 pairs of female obese identical twins Age: 39+1.7 y Author Conclusion: "The high correlation in metabolic efficiency within twin pairs in response to therapeutic weight loss suggests a strong genetic contribution." That does not mean caloric intake and exercise do nothing, but as the data shows, CICO still rules. The textbook authors are lying pigs. The study they cited had nothing to do with supporting their claim: OBJECTIVE: To assess the genetic contribution to determinants of therapeutic weight loss in obese female identical twins. DESIGN: Subjects were studied for 40 days on an inpatient unit in three phases: 7 baseline days; 28 days of weight reduction by a very low calorie diet (1.6 MJ per day); and 5 days after weight reduction.