Diets -> low carb

Question 1

Our understanding of the benefits, safety and long-term efficacy of particular weight-loss diets is limited by significant methodological shortcomings. Explain, in brief, THREE such issues specifically relating to energy restricted diets.

Question 2

popularity and rationale for LC diets

Answer 2

Rationale (Mooradian 2020):
- CHO promote weight gain (insulin release and hunger);
- Glycaemic load and adverse long-term health effects;
- Refined CHO promote obesity and comorbidities.

Question 3

Effect of diet[s] high in sugar, refined carbohydrates, and high glycaemic index

Answer 3

have negative effects on cardiometabolic health and cardiovascular events.”

Question 4

high intakes of dietary fibre and whole grains are

Answer 4

associated with positive effects on metabolic health and cardiovascular
events…”

Question 5

types of dietry fibre

Answer 5

Gel forming
- primary sol fibre
- regulate body glucose
- increase satiety
-CVD benifits

fermentable
- sol/insol. fibres
- ferm. in intestine to produce benificial metabolites
- regulate body glucose

bulk
- insol. fibres
- provide bulk
- speed up transit time
- regulate blood glusoce

Question 6

What are ‘low-carb’ diets?(Mooradian 2020)

Answer 6

No consensus definition
Suggested
LC = CHO <45% kcal
~200g CHO/d
VLC = CHO <10% kcal
To induce ketosis
20-50g CHO/d

Atkins
Induction: 14d crash ketogenic diet (<20g net carbs/d)
Ongoing weight-loss: 2wk-2m (incr. net carbs by 5g/d until upper threshold of continued weight loss
Pre-maintenance: what exceptions can I make?
Lifetime maintenance: highest CHO to prevent weight gain

South Beach
Eliminate all starch & sugar (2wks)
Add ‘goody-carbs’: F&V, wholegrains
Maintenance – dieters should be knowledgeable enough to cope

Zone
individual protein requirements’ & ratioing protein to carbs (7.5:10g) eventually reaching a 40-30-30 diet (C:P:F)

Question 7

What replaces the CHO IN LC diets?(Fechner et al. 2020)

Answer 7

CHO is replaced by either fat, protein or both (expressed as E%)

Question 8

what about in very low carbohydrate diets?(Fechner et al. 2020)

Answer 8

Increased reliance on fat to replace CHO (expressed as E%)

Question 9

Energy Substrates on Low-carb Diets(Macedo et al. 2021)

Answer 9

Body uses glucose for other ATP for energy for muscles and brain

Question 10

IS WEIGHT LOST ON LCDs?
(Fechner et al. 2020)

Answer 10

Combined effect sig. weight loss (−1.34 kg, 95% CI −2.26 to −0.42 kg, p = 0.004) – NS between groups.

BUT
Not all studies found weight changed
Sometimes weight loss was comparable between groups
Often modification of dietary composition resulted in reduction in Energy intake

Question 11

How does Low Carb compare to Low Fat/ Low Energy?

Answer 11

“Further research is warranted to validate the physiological effect of VLCD over longer periods of time…” (Volek et al 2004)

Lim et al 2010
RCT comparing isocaloric VLC(60% fat/CHO 4%), VLF (very low fat, 10%), HUF (high unsaturated fat, 30%) to no intervention

n=113 (BMI M=32±6kg/m2), ♀♂
3mo intense support, 12mo minimal support
Sig. ↓ sys BP and BW in diet groups compared to control

NS diff. in CV risk factors between diet groups
CV risk factors sig. reduced equally across diet groups compared to exacerbation in control group over 15mo

Question 12

Low Carb or Low GI?

Answer 12

GI describes how carbohydrate containing foods effect blood glucose concentrations after consumption (typically within 2h; Zafar 2019).
Glycaemic index is measured in a test food standardised to provide 50g CHO: foods that contain no CHO have no GI.
LCDs focus on reducing the amount of CHO-containing foods in the diet.

There has been a narrow focus on CHO quantity over quality (Sievenpiper 2020)
Reducing glycaemic load of the diet (the amount of CHO containing foods we eat) fails to acknowledge the importance of some CHO-containing foods for health
wholegrains, fruit, vegetables, fibre and legumes (pulses)

Question 13

are low cho diets ketogenic diets?

Answer 13

Ketosis is induced in severely restrictive LC diets (<50g CHO/d)
Can curb appetite
BUT: nausea; fatigue water/ electrolyte loss; limits exercise capacity; halitosis (Mooradian 2020)
LC + high animal protein = disproportionate use of fat stores for energy
Even without weight loss, ketosis is consistent finding (Kappagoda et al, 2004)
Ketosis DOES NOT induce weight loss!
Determining ketosis
ß-hydroxybutyrate is a ketone biomarker (ketosis)
Or measure urinary ketones (ketonuria)

Question 14

Is Initial rapid Weight Loss Water?

Answer 14

In week 1 of a LC diet 2-3kg can be lost
Diet-induced diuresis (Denke, 2001)
Glycogen mobilisation: from liver (~100g) & muscles (~400g)
Each g of glycogen is mobilised along with 2g of water. Around 1kg is lost this way in wk1 – reported as  ‘bloating’.
Ketosis
presence of these nonreabsorbable anions in renal lumen  renal sodium & water loss
“…the rapid weight loss from LC diets is largely by diuresis. After 7-14d, diuresis ends & the phase of rapid weight loss slows” (Bray, 2003)

Question 15

Satiety and Satiation(Landry et al. 2021)

Answer 15

Calorie restriction is not a prescribed feature of LC diets but seems to be an inevitable feature
Both high protein intake & ketosis can suppress appetite
Postulated effects on circulating gut peptides &/or adipocytokines (ghrelin, leptin, CCK…)
Mixed support
Sensory specific satiety?

Question 16

What About Micronutrients?

Answer 16

Exclusion of whole food groups (grains, F & V)  dietary variety along with micronutrients, fibre & phytochemicals

Feasibility of no impact on micronutrient intake on nutritionally replete diets (Tay et al. 2020)

n=61 (completing) adults with type 2 diabetes over 2y
LC = 14E% CHO, 28% protein, 58E% fat
HC = 53E% CHO, 17E% protein, 30E% fat
LCDs can be as restricting in micronutrient intakes as other slimming approaches (Malik et al. 2020)
n=54 (completing) adults over 1y

LC Vs High fibre
“Both groups consumed less than the respective EAR for vitamins D and E and less than the AI for potassium. While a LC diet may be more effective for long-term weight loss, both diets were deficient in micronutrients.”

Question 17

Side effects and possible consequences of LC-HP diets(Adapted from Kappagoda et al 2004; Yancy et al 2004; Westman et al 2002)

Answer 17

Effect + poss cause
Mild dehydration = Water loss & ketosis

Constipation = Lack of dietary fibre

Bad breath = dehydration

Headaches = dehydration

Loss of hair = Nutritional deficiency

Malnutrition = Caloric deprivation

Long-term, e.g. cancer = Low fibre & phytochemicals

Osteoporosis/fractures = Incr. rate of bone loss

Renal insufficiency = Reduced GFR

Question 18

Methodological Short-comings

Answer 18

Landry et al. 2021
Terminology and consistency in regimen
Carbohydrate source often undisclosed/ unmeasured
Generalisability to long-term dietary restriction
Fair comparison to control groups

Question 19

The Future

Answer 19

“…publication acceptance and citations appear to favour apparently larger effect sizes above methodological quality.

Better quality reviews and RCTs are needed, before recommending low-carbohydrate diets as preferred to other approaches for energy restriction.” (Churuangsuk et al. 2018)

The ‘Eco-Atkins’, a plant-based version of Atkins
“…harmful associations may depend on the food source (e.g., animal-based vs. plant-based foods).” (Macedo et al. 2021)

Question 20

Low carbohydrate In summary

Answer 20

“LCD may decrease body mass, waist circumference, and improve fat and carbohydrate metabolism.

When combined with exercise, LCD seems to be an effective strategy in regulating metabolic factors of cardiovascular diseases.

Conversely, LCD may be associated with higher mortality and metabolic dysregulations if it contains large amounts of animal-based foods, particularly saturated fat.”
(Macedo et al. 2021)