Effects of a high protein diet on body weight and comorbidities associated
Baker IDI Heart and Diabetes Institute, Room P5-16 Playford Building, University of South Australia, Frome Rd,
Adelaide 5000, SA, Australia
(Submitted 30 August 2011 – Final revision received 22 March 2012 – Accepted 30 March 2012)
Red meat intake has been frequently associated with the development of coronary artery disease and type 2 diabetes but vegetable protein
has been associated with protection from these diseases. Whether this is related to the protein per se or to the increased polyunsaturated fat
or higher fibre levels associated with more vegetarian diets is not clear.
High protein diets are associated with greater satiety and in some studies are associated with greater weight loss compared with high
carbohydrate diets especially in an ad libitum design. These diets also lower plasma triglyceride and blood pressure and sometimes
spare lean mass. There appear to be no harmful effects of high protein diets on bone density or renal function in weight loss studies.
Key words: Dietary protein: heart disease: type 2 diabetes: weight loss: satiety
The first literature on high protein weight loss diets that were
not liquid, very low calorie diets appeared in 1994. Since then
there has been an explosion of interest in high protein diets,
prompted by the books on the Atkins diet, although scientific
reports on the efficacy of this diet did not appear till much
later. High protein weight loss diets have been described in
the popular literature since the 1890’s.
This contribution focuses predominantly on studies that
have a duration of twelve months or longer and examines
the effects of high protein diets on glycaemic control, hyper-
tension and hyperlipidaemia. There are many issues that
complicate the interpretation of the results, including whether
the protein replaces carbohydrate or fat (this may be one of the
most critical issues), whether the carbohydrate level is low or
very low, thus inducing ketosis, whether the protein is
animal or vegetable in origin and whether the absolute level
of protein is increased (rather than just the percentage of
energy from protein) compared to the usual weight stable diet.
Body Weight and Heart Disease.
There is a limited amount of epidemiological data relating
dietary protein intake to body weight, type 2 diabetes and
cardiovascular disease. In a recent publication from 5 of the
countries in the European Prospective Investigation into
Cancer and Nutrition (EPIC) study a higher intake of protein
from red and processed meat and chicken, rather than fish
or dairy was associated with a greater body weight gain
over 6·5 years, especially in women. There were no associ-
ations with plant protein. Whether the gain was due to fat
or muscle was not clear but there was no clear association
with changes in waist circumference suggesting that central
fat was not increasing(1).The mechanism of the association
was not clear but it did not appear to operate via glycaemic
load changes(2). Similar changes were seen in all 10 countries
in the EPIC-Panacea study(3). Red meat but not protein in
general appears to be associated with heart disease in some
data sets. In the Nurses Health Study, over a 26 year follow
up, red meat, both fresh and processed and high fat dairy
were associated with an increased risk of coronary heart dis-
ease (CHD) while poultry, nuts and fish were associated
with a lower risk. Swapping a serve of nuts, low fat dairy,
poultry or fish leads to 13–30% lower risk of CHD(4). In the
Health Professionals Follow-Up Study neither total protein
or animal or vegetable protein were associated with CHD.
However if the subjects were free of hypertension, hyper-
cholesterolaemia, and diabetes at baseline (very post hoc and
not a pre specified analysis), the relative risk (RR) of CHD
was 1·21 (P for trend¼0·02) for total protein, 1·25 (P for
trend¼0·02) for animal protein, and 0·93 (P for trend¼0·65)
for vegetable protein(5).
*Corresponding author: P. Clifton, email Peter.email@example.com
British Journal of Nutrition (2012), 108, S122–S129
q The Author 2012
British Journal of Nutrition
Type 2 diabetes
As with heart disease there has been some degree of associ-
ation reported for a variety of red meats and an increased
risk of type 2 diabetes. In only one study (the MASALA
study), a small study of Indians in San Francisco, was the
intake of total protein associated with an increased risk of
type 2 diabetes (70% increase in risk in the highest intake
group)(6). In the IRAS study red meat, eggs, cheese and
cottage cheese were associated with an increased risk of
type 2 diabetes(7). Both of these studies were small with
only 144 and 880 participants, respectively. In the Whitehall
study burgers and sausages increased the risk of type 2
DM(8)as did total red and processed meat and hot dogs
and bacon in the Nurses health Study with risk ratios varying
from 1·26 to 1·73(9). Murakami showed that heme iron
intake was a predictor of type 2 DM in a meta analysis of
15 cohort studies(10). A recent meta analysis of 12 cohort
studies showed a modest increase in risk of type 2 DM
with red meat and processed meat with RRs of 1·21 to 1·41
from highest to lowest intake categories, but there was con-
siderable heterogeneity(11). These findings contrast with the
association of a high glycaemic load diet with about a 50%
increase in the risk of type 2 DM in US Nurses(12). In this
group the low glycaemic load diet contained about 5%
more protein and about 15% more fat. In a further analysis
of the Nurses data Halton 2008(13)showed that a low carbo-
hydrate diet based on vegetable protein and vegetable fat
were protective with an 18% reduction in the risk of type 2
DM comparing extreme deciles while animal protein and
animal fat was not protective.
In contrast in the EPIC-Potsdam cohort, substituting 5%
of energy as protein for carbohydrate reduced the risk of
type 2 DM by 23%(14)while in the Attica study total protein
was unrelated to fasting glucose and insulin, but red meat
was associated with increased levels of both glucose and
Overview of the epidemiological literature
Although red meat appears to be associated with both
heart disease and type 2 diabetes in virtually all studies
consumers of a large amount of red meat tend to be more
obese, smoke more and exercise less so they are clearly
a special group. Even though all studies are adjusted
for these confounders it is possible there are unmeasured
behavioural confounders that account for the relationship
observed that persist after adjustment for saturated fat.
There does not appear to be a good biological explanation
for the association.
Interventions with high protein weight loss diets
The major problem with interpreting all of the weight loss
studies is that weight loss per se has the most powerful effect
on the comorbidities which leaves little room to see an effect
Body weight and CVD risk markers
Only the most important large and long term studies will be
discussed in detail.
The largest test of a high protein diet was performed in the
USA in a 4 centre trial(16)In the study 811 participants were ran-
domly assigned for 2 years to one of 4 possible diets: 20% of
protein); 20% 25%, and 55% (high protein); 40%, 15%, and
45% (high fat, average protein); 40%, 25%, and 35% (high fat,
high protein). The design was a 2 by 2 factorial and each diet
was prescribed with a 750kcal deficit based on calculated rest-
ing energy expenditure and activity level. At 6 months an aver-
age of 6kg weight loss (7%) occurred which when compared
with other trials was relatively low. Subjects began to regain
weight after 12 months and by 2 years weight loss was between
3–4kg with no statistically significant differences between
groups. At two years, on intention-to-treat analysis, weight
loss was 3·0 and 3·6kg in the 15% and 25% protein groups,
respectively. In the completers (645 out of 811) it was 3·6 and
4·5kg (P¼0·11). In the 20% fat and 40% fat groups it was
3·3kg for both and in the contrast of the 65% vs 35% carbo-
hydrate groups it was 2·9 and 3·4kg, respectively. Weight loss
was 0·2kg per support session attended.
Compliance to a high protein diet increased weight loss from
3kg to 8kg as the protein intake increased from 15% to 25%
(Fig. 1). The number of sessions attended also increased from
42% to 59% and the authors attributed the increased weight
loss to attending the counselling sessions (0·2kg per session
attended over the 2 years) but an equally valid interpretation is
that the volunteers who liked the diet were much more compli-
ant to it and because of this attended more sessions. Unfortu-
nately there was no multivariate analysis incorporating both
weight loss, possibly because the target protein of 14·5% was
achieved compared with an achieved level of 24% in the
group who attended fewer sessions, suggesting that the higher
protein diet per se was beneficial. Urinary nitrogen measures
showed that the difference in protein intake was 10g at
6 months and 5g at 2 years rather than the 20g target (which
in itself was relatively modest) so compliance to the prescribed
diet was relatively poor in this study although there was only a
20% dropout rate over the 2 years which is far fewer than
might be expected. Based on HDL cholesterol changes differ-
ences in carbohydrate intake were only 6% rather than the
expected 30% difference.
All diets reduced cardiovascular risk factors for cardio-
vascular disease and diabetes at 2 years. The low fat and
high carbohydrate diets reduced LDL cholesterol more than
the high fat diets and low carbohydrate diets 5–6% vs 1%.
Triglyceride was lowered by 12–17% and there was no
statistically significant greater effects in the low carbohydrate
diet groups. This was almost certainly a result of small differ-
ences in achieved carbohydrate intake.
The main outcome from this study was that it was imposs-
ible to maintain significant macronutrient differences long
term. What little differences were achieved had no effect.
Effects of a high protein diet on body weightS123
British Journal of Nutrition
In the DIRECT 2 year weight loss study, 322 moderately
obese participants (mean BMI 31, 86% men) were randomized
to one of three groups: low-fat, Mediterranean, or low-
carbohydrate diets(17,18); 84·6% completed the study. In
the intention-to-treat analysis, weight loss was 2·9 ^ 4·2kg
for the low-fat diet, 4·4 ^ 6·0kg for Mediterranean, and
4·7 ^ 6·5kgfor low-carbohydrate
P,0·001). Weight loss among the 272 participants who
completed thetwo-year intervention
4·6 ^ 6·0kg, and 5·5 ^ 7·0kg, respectively. Men lost more
weight on the low-carbohydrate diet, but women lost more
weight on the Mediterranean diet (P for group£sex , 0·001)
suggesting that dietary preference may have a role to play in
successful weight loss.
Overall compliance at 2 years was 90% in the low-fat, 85%
in the Mediterranean, and 78% in the low-carbohydrate diet
(diet-group £ time
was3·3 ^ 4·1kg,
groups (P¼·042 between groups). Dropout rates differed
between the diets, 9·6% for the low fat group, 14·7% for
the Mediterranean and 22% for the low-carbohydrate group
(P¼·04 between the diet groups). In a multivariate model,
significant independent predictors of dropping-out were:
higher baseline BMI (OR ¼ 1·11) and lower weight loss at
6 months (OR ¼ 1·20). Greater weight loss achieved at
month 6 was the main predictor associated with success in
weight loss (.5%) over 2 years (OR ¼ 1·5) suggesting that
in the short-term a more restrictive diet may be the best
option. In those who achieved a .5% weight loss at 2 years
(42% of the group) weight loss at 6 months was 9·3kg while
the failures (,5% weight loss) only achieved a weight
loss of 3·2kg at this time point. Self-reported complete
adherence score to diet was greater on a low-carbohydrate
diet (P,0·05 compared to low-fat) until month 6, but
dropped overall from 81% at month 1 to 57% at month 24.
This suggests that the low carbohydrate, high protein diet is
best used for no more than 6–12 months with a change to
another dietary pattern for long term weight maintenance.
Although the % protein increased in the Atkins diet by 3·1%
of energy, absolute protein intake decreased by 7–20g/day.
As this was a workplace feeding study in the Negev desert
its general applicability may be limited as it was much easier
in this setting to maintain macronutrient differences but
again the absolute differences achieved in weight outcomes
were not large.
Foster et al.(19)compared a low carbohydrate diet to a low
fat diet over 2 years. Weight loss was approximately 11kg
(11%) at 1 year and 7kg (7%) at 2 years. There were no differ-
ences in weight, body composition, or bone mineral density
between the groups at any time point. The number of partici-
pants commencing the study was 307 and 32% dropped out in
the low fat group and 42% in the low carbohydrate group.
Long term follow up of the ad libitum 6 month Astrup
In this Danish study 65 healthy, overweight and obese sub-
jects were placed on either a high carbohydrate (HC 58%
carbohydrate, protein 12%) or a high protein (HP 45% carbo-
hydrate, 25% protein) diet (6) with no guidance on energy
intake and all food was provided by self-selection in a study
shop. Weight loss after six months was 5·1kg in the HC
group and 8·9kg in the HP group (P,0·001), and fat loss
was 4·3kg and 7·6kg, respectively (P,0·0001), whereas no
changes occurred in the control group. More subjects lost
.10kg in the HP group (35%) than in the HC group
(9%)(20). Similar results were seen in this group at 1 and
2 years, with more participants in the HP group (17%)
having lost .10kg than in the HC (P,0·09). At 24 months,
both groups tended to maintain their 12 months weight loss,
but more than 50% were lost to follow-up(21).
Dansinger et al.(22)compared Atkins (low carbohydrate),
Zone (high protein), Weight Watchers (calorie controlled)
and Ornish (low fat), in 160 participants with fairly poor
results at 12 months with no group exceeding a 3kg average
weight loss. Changes in TC/HDL ratio, insulin and CRP were
directly related to the amount of weight lost and did not
differ by diet type.
15 17 19
Protein (% kcal)
21 23 25
Weight loss (kg)
Sessions attended (%)
1416 18 20 22 2426
Protein (% kcal)
Weight loss (kg)
Sessions attended (%)
54·0 47·8 56·057·348·7
Fig. 1. Weight loss as a function of compliance and protein intake (redrawn
British Journal of Nutrition
Similar diets were tested in 311 pre-menopausal women for
1 year(23)Between 35–50% of all subjects had dropped out
by 12 months. Mean 12-month weight loss was: Atkins,
4·7kg, Zone, 1·6kg, LEARN (a calorie controlled behavioural
program), 2·6kg and Ornish, 2·2kg. Weight loss was not
statistically significantly different among the Zone, LEARN,
and Ornish groups but Atkins was different to the Zone
diet only (P,0·05) suggesting that either satisfaction with
the Atkins diet or more restricted food carbohydrate choices
are important during weight loss(24). Adherence to the diet
was not predicted by age, BMI or education level(25).
carbohydrate (high protein) or low-calorie, high-carbohydrate,
low-fat diets. A difference in weight loss was seen at 6 months
but not 12 months which was very similar to the results of
Samaha et al.(26,27). Brehm et al.(28)and Yancy et al.(29)
showed better results at 6 months on a high protein low
carbohydrate diet but did not extend the studies to 12 months.
McAuley et al.(30,31)contrasted 3 different diets of varying fat
and protein levels. The high fat diet produced rises in LDL
cholesterol in 20% of the group despite the weight loss.
Overall in these 12–24 month studies there was little benefit
from a high protein diet either with a moderate or a high
carbohydrate diet even when compliance to the diet was
achieved. There were few differences in cardiovascular risk
In a meta-analysis by Nordmann et al.(32)five trials of the
Atkins diet with a total of 447 individuals followed up for at
least 6 months with intention-to-treat analysis were evaluated.
After 6 months, individuals assigned to low-carbohydrate diets
lost more weight than those on low-fat diets (weighted mean
difference (WMD, 23·3kg). This difference was no longer
HDL-cholesterol values changed more favourably in individ-
uals on low-carbohydrate diets after 6 months but total
and LDL-cholesterol values changed more favourably on a
low-fat diet. There were no differences in blood pressure
Thus a high protein, low carbohydrate high fat diet does not
enhance weight loss but has adverse effects on the most import-
ant lipid species-LDL cholesterol.
Krieger et al.(33)examined 87 short term studies (some con-
trolled and some ad libitum) finding that protein intakes of
.1·05g/kg body weight were associated with 0·6kg better
retention of lean mass and in studies greater than 12 weeks
in duration this increased to 1·2kg. In studies with a carbo-
hydrate intake of ,35–41% there was a 2kg greater loss of
fat mass, but this was accompanied by a 0·7kg greater loss
of lean mass. In studies of 12 weeks or more this increased
to 5·6kg and 1·7kg respectively.
Although lean mass my be better preserved on high protein
diets the physiological significance of this finding is not clear
as there are no benefits of a high protein diet on glucose levels.
In a study from our group at CSIRO of overweight and
obese women(n ¼ 100)
(.1·5mmol/L, n ¼ 50) lost more fat mass with the high pro-
tein than with the high carbohydrate diet (6·4 and 3·4kg,
respectively; P¼0·035)(34). In a 12 month follow-up of this
subjects toeither low-
thosewith high serum TG
study women who reported eating more than 90g/day of pro-
tein were 3kg lighter than women eating less than this
amount. Protein intake was confirmed by urinary urea:creati-
nine ratio(35). In a pooled analysis of data from 3 studies in
overweight non diabetic subjects (n ¼ 215) subgroup analysis
showed that subjects with serum TG . 1·7mmol/L lost more
total fat (high protein diet 6·17 ^ 0·50; standard protein diet
4·52 ^ 0·52, P¼0·012) and abdominal fat (high protein diet
1·92 ^ 0·17; standard protein diet 1·23 ^ 0·19, P¼0·005)
when on a high protein diet(36).
We have completed a large 12 month, energy controlled test
of an Atkins style weight loss diet compared with a high
carbohydrate weight loss diet particularly focused on vascular
measures(37,38). Sixty-nine participants (59%) completed the
trial: 33 in the LC group and 36 in the LF group. Both
groups lost similar amounts of weight (LC: 14·5 ^ 1·7kg;
LF: 11·5 ^ 1·2kg;P¼0·14,
(LC: 11·3 ^ 1·5kg; LF: 9·4 ^ 1·2kg; P ¼ 0·30). Blood pressure,
fasting glucose, insulin, insulin resistance, and C-reactive pro-
tein decreased independently of diet composition. Compared
with the LF group, the LC group had greater decreases in tri-
glycerides (0·36 ^ 0·15mmol/L; 95% CI: 0·67, 20·05mmol/L;
P¼0·011), increases in HDL cholesterol (0·23 ^ 0·09mmol/L;
95% CI: 0·06, 0·40mmol/L; P¼0·018) and LDL cholesterol
(0·6 ^ 0·2mmol/L; 95% CI: 0·2, 1·0mmol/L; P ¼ 0·001), and
a greater but nonsignificant increase in apolipoprotein
B (0·08 ^ 0·04g/L; 95% CI: 20·004, 0·171g/L; P¼0·17.
There was a significant time £ diet effect for flow mediated
(5·7 ^ 0·7% to 3·7 ^ 0·5%) but remained unchanged in LF
(5·9 ^ 0·5% to 5·5 ^ 0·7%). Pulse wave velocity improved
in both groups with no diet effect (P¼0·80). Thus the high
saturated fat, high protein diet produced excellent weight
loss but produced adverse effects on LDL cholesterol which
Layman et al.(39)in a 12 month study in 130 obese adults
found that a high protein diet reduced fat mass more than a
high carbohydrate diet although overall weight loss was the
same. The protein diet had sustained favourable effects on
serum triglyceride, HDL cholesterol (HDL-C), and TAG:HDL-C
compared with the high carbohydrate diet at 4 and 12 mo
In high protein diets that are low in fat and moderate
in carbohydrate some benefits are seen in terms of body compo-
sition, HDL and TG without adverse effects on LDL cholesterol.
time £ diet)and body fat
FMD decreased inLC
Weight maintenance studies
High protein diets have been tested by several groups follow-
ing weight loss with a very low calorie diet. Several groups
have examined this question and produced conflicting
answers. A recent large study (548 participants) from Europe
by Larsen et al.(40)of diet composition in weight maintenance
for 6 months showed that a modest increase in protein led to a
0·93kg weight difference compared with normal protein and a
modest reduction in glycaemic index led to a 0·95kg weight
difference compared with a high glycaemic index diet and
these two strategies were additive and also produce fewer
Effects of a high protein diet on body weight S125
British Journal of Nutrition
drop outs (26% versus 37%). This study has also shown that
advising people to increase their protein intake is relatively
ineffective in both achieving an increase in protein and enhan-
cing weight maintenance, whereas providing high protein
foods (as was done in 2 centres only out of the 8 centres in
the study) is effective as has been previously shown. The
reverse was shown with GI: providing low GI foods was inef-
fective relative to high GI foods, while asking people to
choose low GI foods enhanced dietary compliance. This find-
ing suggests the GI of foods per se has no impact on weight
maintenance which differs from the authors’ conclusions.
However others have shown that high protein produces no
benefit in weight maintenance at 12 months after an 8 week
very low calorie weight loss phase(40)although only 47% of
subjects completed the study. We have shown that a higher
protein diet (.88g/d) is worth about 3·1kg extra body
weight loss at 12 months compared with a lower protein
Lejeune et al.(42)found that a 20% increase in protein intake
(through an unmatched supplement) during weight mainten-
ance after a 4 week weight loss period reduced weight
regain by 50% over the subsequent 3 months. Claessens
et al.(43)found a similar effect using a matched casein sup-
plement over 12 weeks of weight maintenance which was
worth 2·2kg of fat. Layman et al.(39)found that a weight loss
diet that had double the amount of protein (1·6g/kg vs
0·8g/kg) led to better body composition at both 4 months
and 12 months, especially in those participants who lost
more than 10% of their body weight over this period.
There appears to be some evidence that a high protein diet
helps maintain weight loss especially in people who have
had good initial weight loss.
Type 2 Diabetes and glucose control with high protein,
low carbohydrate diets
Short term weight stable studies conducted by Nuttall and
Gannon(44–48)over the last few years have demonstrated
very impressive reductions in HbA1c with a reduction in
carbohydrate of 25% energy with replacement with fat and
protein (15% to 30%). These reductions were of the order
of a 35% fall in area under the glucose curve and a 25% fall
in Hba1c over 10 weeks. These studies used a very small
number of participants (6–12) and all food was provided.
Similarly a 14 day inpatient study of a low carbohydrate diet
in 10 obese patients with type 2 DM. led to a fall in Hba1c
from 7·3 to 6·8%. Energy intake decreased from 3111 to
2164kcal/d and insulin sensitivity improved by 75%, with
triglyceride falling by 75%(49).
In a meta analysis of 19 trials which exchanged carbo-
hydrate with fat with a median carbohydrate reduction of
18%, Kodama et al.(50)found much smaller effects than Nuttall
and Gannon with 2 hour glucose 10% higher with the higher
carbohydrate diet and fasting and 2 hour insulin 8–13%
higher. As expected fasting triglyceride was 13% higher
and HDL 6% lower with the high carbohydrate diet. In the
306 participants HbA1c, fasting glucose and LDL were not
different probably because the trials were all of short duration
(10 days to 6 weeks) although Nuttal and Gannon have shown
significant effects on Hba1c even in 5 weeks. Whether the
exchange of carbohydrate with both protein and fat that
their design uses is a significant factor is not clear. Another
meta analysis from Kirk et al.(51)
Nuttall and Gannon studies in its 263 participants from US
and Canadian studies showed that HbA1c, fasting glucose
and triglyceride were lower on a low carbohydrate diet
which often included a higher protein level (in 7 studies).
The longest study was 6 months duration and the rest were
1–16 weeks long.
However with free living volunteers purchasing and cook-
ing their own food for many months the reality is quite differ-
ent. In a New Zealand 6 month study with 93 participants on
oral hypoglycaemics and or insulin a lower carbohydrate diet
reduced weight by 1·3kg and HbA1c by 0·4% compared with
a control group. Saturated fat fell by 2% and protein increased
by 1·6%(52). Ten patients from the intervention group had a
reduction in medication compared with two in the control
group while there were ten more patients in the control
group compared with the intervention group with an increase
in medications so the true difference from the intervention
in HbA1c would be greater. Nevertheless the weight loss is
disappointing despite 7 individual counselling sessions and a
group session as well as phone support.
A recent 12 month weight loss study from Baker IDI
Australia which included 98 people with type 2 diabetes com-
pared a high protein diet with a high carbohydrate diet(53).
Weight loss at 12 months was small, 2–3kg, with small
changes in HbA1c of 20·2 2 ·3% with no differences
between diets. Although reported energy intake dropped by
about 25% from baseline to 12 months the weight loss clearly
did not match this. Reported changes in macronutrient
composition were small (3–5%) and protein differences at
12 months as assessed by 24 hour urinary urea were not
statistically significant. Weight loss was related to reported
compliance to the diets. Participants with the highest self
management score lost 5·5kg and lowered their HbA1c by
0·87% while participants with the lowest score had no
changes in either variable. The study clearly showed the
difficulty of implementing a weight loss strategy for partici-
pants with type 2 diabetes in a routine clinical environment.
In contrast another 6 month hospital based study in North
Carolina achieved a weight loss of 11·1kg and a reduction
in HbA1c of 1·5% with an Atkins diet(54). The calorie-reduced
low GI control group also did very well with a weight loss of
6·9Kg and an HbA1c fall of 0·5%. Medications were reduced
substantially in both groups but 42% of volunteers dropped
out. A study in New York with 105 participants produced
much lower weight loss (3·4%) at 12 months with no differ-
ences between the low carbohydrate and low fat diets and
no changes in HbA1c(55). Similarly in a general practice
study 144 participants were enrolled in a test of an Atkins
diet compared with a low fat diet for 2 years. Only about
50% returned at 2 years but records could be extracted
for another 57. There was a minor weight loss which
did not differ by diet and no changes in HbA1c at 6,12 or
24 months(56). A Canadian study that reduced carbohydrate
which included the
British Journal of Nutrition
by 13% for 6 months had no effects on body weight or
People with type 2 diabetes have a better weight and lipid
profile at 1 year after following a 12 week high protein diet
compared with those who followed a high carbohydrate
Although a lower carbohydrate, higher protein diet may
lower HbA1c in some studies the effects in others is unexpect-
Acute single meal effects of protein on glycaemic control
Eight type 2 diabetic patients each ingested 350ml beef soup
30min before a potato meal; 55g whey was added to either
the soup (whey preload) or potato (whey in meal) or no
whey was given. Gastric emptying was slowest after the
whey preload (P,0·0005). The incremental area under the
blood glucose curve was lower after the whey preload
and whey in meal than after no whey (P,0·005). Plasma
glucose-dependent insulinotropic polypeptide, insulin, and
cholecystokinin concentrations were higher on both whey
treatments than after no whey, whereas glucagon-like peptide
1 was greatest after the whey preload (P,0·05). These data
suggest that protein has more significant effects on glucose
homeostasis other than just replacing carbohydrate(59). Much
more research needs to be done in this area, especially in
long term weight stable studies.
Preservation of lean mass
Much attention has been focused on the ability of a high pro-
tein diet to reduce the amount of lean tissue lost during weight
loss. Krieger(33)in his meta analysis of high protein, reduced
carbohydrate diets found that a daily protein intake of
1·05g/kg preserved about 0·6kg of lean mass more than a
lower protein diet. In studies longer than 12 weeks (7 studies
only) the difference increased to 1·2kg. There were no effects
on fat mass. In an unpublished meta analysis we have
examined 29 studies with a duration of 12 weeks or longer
and found no difference on lean mass loss between high
and normal protein weight loss diets although there were
small but statistically significant effects on fat mass.
Donald Layman has been a very strong advocate of high
protein diets for lean mass preservation and believes that an
intake of 2·5g of the essential branched chain amino acid leu-
cine is required at each meal with a minimum of 10g/day(60).
In his 12 month study of a comparison of a protein intake of
1·6g/kg (carbohydrate/protein ratio of ,1·5) vs 0·8g/kg
(carbohydrate/protein ratio of .3·2) absolute lean mass loss
was the same in each group (2·6 and 2·7kg) but change in
% fat mass loss differed (5% vs 3%) so that there was a relative
sparing of lean mass compared with fat mass with a 2kg
greater fat loss in the high protein group(38). Whether
this difference in lean and fat mass translates into clinical
differences in insulin sensitivity and glucose control is not
clear as the evidence is quite contradictory with increases in
fasting glucose(61)as well as no change relative to a high
In weight stable studies Hodgson et al.(62)have demonstrated
that an increase in protein of about 5% of energy in exchange
for carbohydrate lowers BP by about 5mm Hg in hypertensive
people. The OmniHeart study showed similar effects (3·5mm
Hg in hypertensives(63).
Although a high protein weight loss diet over 12 weeks had
no beneficial effects on insulin sensitivity or HbA1c, it did
lower blood pressure quite significantly (10/18mm Hg) even
though weight loss was small and not different from the
high carbohydrate diet (2·3 and 2·5kg)(64).
It is commonly stated that a high protein diet could potentially
reduce bone density and have adverse effects on kidney
function, particularly in those with kidney disease. We have
shown no adverse effects of a high protein diet in a 2 year
weight loss study in postmenopausal women and no adverse
effects on renal function in 40 patients with type 2 diabetes
and microalbuminuria in a one year weight loss study
(P. Clifton, unpublished data).
High protein diets (ad libitum or energy controlled) increase
the loss of fat mass relative to lean mass in many studies
with a clear reduction in plasma triglyceride. The rise in
HDL cholesterol seen with high protein Atkins style diets
may not be beneficial for vascular function and high saturated
fat versions of the low carbohydrate diets should be avoided.
Replacement of carbohydrate with protein lowers glucose and
improves HbA1c and is worth considering as a dietary option
in type 2 diabetes.
The author states there is no conflict of interest.
This research received no specific grant from any funding
agency in the public, commercial or not-for-profit sectors.
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