Diet -> low calorie diet

Question 1

energy balance (astrup & tremblay, 2009)

Answer 1

Homeostatic regulation in place to maintain body weight and body energy stores
regulation of food intake occurs through interaction between hormones, neuroendocrine factors, CNS and body organs (e.g. brain and liver) influencing hunger and satiety
influenced by the wider environment
energy balance occurs over longer term when the energy content of food consumed = energy expenditure despite short term fluctuations in energy intake and expenditure

Even a small chronic positive energy balance (intake > expenditure) due to dysregulation in energy balance results in increase in overall body energy stores
preferential storage of excess energy as fat
ultimately leading to overweight and obesity

Weight loss therefore requires a state of negative energy balance (caloric restriction to below metabolic requirements)

Question 2

adult overweight and obesity in England(NHS digital, 2020)

Answer 2

This equates to 12.6m adults in England living with obesity and a further 16.3m adults overweight

Significant increase from 1993 figures (~15% adults with obesity)

Question 3

health effects of excess weight

Answer 3

increased risk of wide range of chronic health conditions
CVD
type 2 diabetes
some cancers
gallbladder disease
gout
osteoarthritis
depression

Question 4

prevalence of reported dieting

Answer 4

Piernas et al. (2016):
47% British adults reported trying to lose weight in 2013 Health Survey for England
Reported weight loss attempts higher for those classed as overweight (53%) or obese (76%)
But, 10% of people with BMI <18kg/m2 and 30% of people with BMI 22-25kg/m2 also reported attempting to lose weight

Question 5

calorie deficit diets (NICE, 2022)

Answer 5

Calorie/energy deficit diet
reduction in energy intake relative to requirements (generally calculated as ~600 kcal/day deficit)
can involve varying macronutrient composition

Low calorie diet (LCD)
800-1600 kcal/day

Very low calorie diet (VLCD)
<800kcal/day with high protein to preserve muscle mass – used in limited cases only and with appropriate medical supervision

Question 6

calorie deficit diet examples

Answer 6

Traditionally based on energy-restricted diet low in fat, relatively high in starchy carbohydrate
Rationale: fat more energy dense & less effect on satiety, so low-fat diet can maintain volume of food eaten and reduce energy density with ↑ bulkier starchy foods

Typical ‘low fat diet’ (LFD)
CHO: 50-60%
Protein: 15%
Fat: 25-35%
Saturated fat <10%

Weight watchers
energy restricted to achieve 0.5-1.0kg weight loss/week

slimfast
Meal replacement products (MR); 1200-1400kcal/d

Question 7

low-fat diets as a calorie deficit diet – landmark studies

Answer 7

Diabetes Prevention programme (Knowler et al. 2002)
3,234 overweight/obese participants with impaired glucose tolerance: lifestyle (<25% energy from fat with caloric restriction to 1200-2000 kcal/d, physical activity, individual coaching) Vs metformin or placebo

Conclusion – highly effective means of delaying/preventing type 2 diabetes but relative contributions of low-fat, calorie restriction and physical activity not determined

Finnish Diabetes Prevention Study (Tuomilehto et al. 2001)
522 overweight/obese subjects with impaired glucose tolerance to intervention (fat <30% energy), saturated fat <10% energy, ↑fibre, physical activity with support) or control

beneficial changes in fasting glucose, plasma glucose after GTT, serum insulin, blood pressure in intervention group
Incidence of diabetes after 4 years = 11% in intervention group and 23% in control group (reduction of 58%)

Question 8

effectiveness of calorie deficit diets (chao et al. 2021)

Answer 8

RCTs comparing VLCDs (<800kcal/d) to LCD (800-1800 kcal/d) induced greater short term (<6 months) weight loss
But, VLCDs did not produce greater long-term weight loss due to greater weight regain (mean 62% of weight lost) than with LCDs (41% of weight lost)
Studies found LCDs can result in weight loss of 5-8kg in 6 months, maintained at 12 months with continued support

Question 9

is macronutrient composition important? (1)

Answer 9

Inpatient feeding studies in ‘metabolic wards’ control energy intake and nutrient composition of diet/measure energy expenditure (i.e. dietary adherence assured)

Average weight loss similar after 2 years regardless of macronutrient composition; equally successful in achieving clinically relevant weight loss
Sacks et al. (2009)

Question 10

meta analysis on macronutrient composition

short vs long term

Answer 10

trials showed weight loss in short term irrespective of whether low carbohydrate or ‘balanced’, and probably no difference in weight loss and CVD risk factors up to 2 years of follow up.
Showed weight loss short term
People found it challenging to stick to diets long term…..

Question 11

adherence to dietary pattern

Answer 11

Calculated adherence scores for low carbohydrate and ‘balanced diet groups – lower score = less deviation from prescribed macronutrient goal (better adherence)
Calculated adherence scores described as ‘variable’
4 trials had similar adherence scores
5 trials had better adherence scores for low carbohydrate diets
4 trails had better adherence scores in the ‘balanced’ diet

If people aren’t following the diet, that when there is a reduction in how successful it will be

Question 12

limitations in existing research comparing diets

Answer 12

• some reviews included both controlled and uncontrolled diets
• if diff, any effects on CVD risk factors could be confounded by co-interventions

Question 13

effectiveness for sustained weight loss

Answer 13

Where there is support, weight loss could be maintained

The mean doesn’t tell us the range and also the individual results = everyone is different

Question 14

factors affecting adherence to weight loss approaches

Answer 14

Dietary adherence is critical to short and long term weight loss and maintenance, but non adherence is often high – therefore, important to understand how to maximise adherence

Question 15

Meal replacement products

Answer 15

Defined in review by Astbury et al. (2019) as: ‘Discrete foods, food products, or drinks used to replace foods usually consumed at one or more meals with the intent to reduce daily energy intake for the purposes of achieving weight loss or weight maintenance following weight loss’

Replace at least one meal a day, and diet includes at least one meal daily comprised of conventional foods

Can include soups, shakes, bars plus portion-controlled ready meals, breakfast cereals etc

Separate to low energy total diet replacement (TDR) products

Such as soups, shakes and bars = easy and more convenient, already preportioned

Question 16

UK example - slimfast

Answer 16

1 shake, 1 meal bar, 3 x Slimfast snacks:

~740 kcal/d (1340 kcal including meal)

£4.61 for products

Question 17

effectiveness of meal replacements for weight loss (Astbury et al. 2019)

Answer 17

Concluded – MR should be considered as a valid option for management of overweight and obesity in community and healthcare settings

Consistent findings with another recently published SR&MA finding greater weight loss with MR Vs food, particularly when >60% daily calories from MR products (Min et al. 2021)

If they are fortified, it might be more beneficial

Question 18

user perceptions of MR diets

Answer 18

easy
quick to understand
quick fix
boring
need for self discipline
feel hungry
anti-social
difficult at weekends and on holidays

Question 19

weight management using MR and T2D remission(lean et al, 2018)

Answer 19

DiRECT: cluster RCT of weight management intervention/control across 49 primary care practices

24% had 15kg weight loss at 12m

weight loss sufficient to achieve T2D remission can be attained in many individuals by use of an evidence-based weight management programme

Question 20

effectiveness of commercial programmes- the ‘diet trials’(1)

Answer 20

Dr Atkins’ new diet revolution (self monitored low carbohydrate diet)

Slim-fast (MR)

Weight Watchers pure points programme (calorie restricted diet and group sessions)

Rosemary Conley’s eat yourself slim diet and fitness plan (low fat diet and weekly exercise class)

Plus control group offered delayed treatment

Initial weight loss more rapid, then slowed – higher initial weight loss in Atkins group, but no difference after 6 months

All 4 diets resulted in significant loss of body fat, weight and waist circumference over 6 months – no sig. difference between groups

Question 21

current uk nice guidance

Answer 21

total energy should be less that expenditure

diets that have 600kcal/day deficit or low fat diets are reccomendded for sustainable weight loss

consider low calorie diets (800-1600) but they will be less nutritionally complete