Do Low-Carb, High Fat Diets Cause Heart Disease – What do the studies say?

I’ve been wondering lately. Is it possible to eat a low-carb, high fat diet without getting heart disease? What does the science say? While the Atkins diet has been around since the 70s there isn’t a ton of research on some of the new low-carb fads like Paleo and Keto.

Still, there’s research out there so let’s see if we can find an answer.

As always with literature reviews, the more you dig into the weeds on this the more you find support for each side of things. You will be the final judge. Scroll down for links and summaries to studies trying to answer this question – Does low-carb, high fat cause heart disease?

I’ll be using this post as a reference point in future blog posts. After reviewing everything there’s a lot of good details here and it’s not as useful to use this review to just make a bold statement.

One of my favorite facts learned is that higher protein levels lead to more weight loss than messing with your carbs. I’ll be using that in future personal diet experiments so stay tuned.

Other key findings from the studies below:

  • Low fat is typically defined as less than 30% fat from total calories. This is not low enough to get results and you can see that in the studies below.
  • Again, higher protein did a better job of reducing weight and fat than restricting carbs
  • Many low-carb studies found more weight loss than low-fat groups. Again, I would like to see them compare low-carb to low-fat as defined as less than 15% calories from fat. Please not the definitions below. Low-carb is defined differently in pretty much every study.
  • Low-carb diets improve cholesterol results when you look at the individual cholesterol pieces like HDL, LDL, etc.
  • Low-carb does not improve LDL levels, the bad cholesterol. Even if you get more good cholesterol on these diets you’re still stuck with high LDL levels which have more of an impact on heart disease later down the road.
  • Low-carb does not improve total cholesterol levels.

Study #1 – “The low-carbohydrate diet and cardiovascular risk factors: Evidence from epidemiologic studies”

I’ll start with a literature review article. This one scanned the literature to answer a very similar question. Let’s see what they found for us:

  • Overview and Methods – For this review they defined low-carbohydrate diets as those where less than 45% of energy comes from carbs. For low-fat diets it assumed less than 30% of energy comes from fat.
    • Side note – While “low-fat” has traditionally been defined as less than 30%, studies find that you don’t really get the good benefits of a low-fat diet until you get under 10% of your calories a day from fat. Let’s leave that for the future since we’re really diving into high fat, low carb questions here.


  • Key findings – Next let’s summarize what they found…


    • Randomized trials found low-carb diets reduced bodyweight 2.1 – 14.3 kg (4 – 30 lbs) over a 6 month period
    • Both fat and lean muscle were lost but most weight loss was from fat [Note – this is one of the key complaints of keto diets, that it’s all water weight, yet this review finds fat loss is a bigger component over 6 months]
    • The 6 month weight loss didn’t last. After 12 months the weight was back.
    • Both ketogenic and non-ketogenic low carb dieters both had reductions in insulin resistance. Neither diet was better
    • Both low-carb and low-fat diets reduced fasting blood sugar levels and other markers for diabetes (HbA1c, serum insulin, and HOMA)
    • Blood pressure went down on any diet that involved weight loss. There were no significant differences on this between diets.
    • Diabetic patients lost the same weight on low carb vs low fat. They also had the same improvements in blood lipids, blood pressure, blood glucose, and plasma insulin after a 1-year followup.
    • Keto diets have been widely used to help reduce seizures in children with epilepsy. A review of the studies found that keto diets in kids with epilepsy had negative cardiovascular effects. There was an increased risk of abnormal heart rythyms, and negative changes to their cholesterol, LDL, and HDL over a 2-year period.
    • Even with Keto or low-carb, red meat, both processed and unprocessed, led to increased risk of heart disease.
    • Fish and poultry did not lead to increased heart disease risk, type 2 diabetes, stroke, and high blood pressure.
    • Those that ate soy at least 5 times per week had 45 – 69% lower risk of heart disease related deaths among Japanese women.
    • Starchy vegetable intake did not lead to less heart disease.
    • The review pointed out that those eating low-carb or keto should focus on getting as much extra fiber from fiber-rich fruit and vegetables, should switch from red meat to poultry and fish, shouldn’t be afraid to add some soy products, and should stay away from starchy vegetables and refined grains.

Study #2 – “Effect of a high-fat ketogenic diet on plasma levels of lipids, lipoproteins, and apolipoproteins in children.”

  • Overview and Methods
    • This study was the one referenced above about looking at the heart health of kids on keto who were using that as an option to control their epileptic seizures.
    • They looked at 141 kids over 6 months who had difficult to control seizures that were placed on keto diets. The followed up after one year and then again after 2 years.


  • Key Findings


    • Total cholesterol went up 58 points in children on keto diets after 6 months
    • LDL cholesterol (the bad cholesterol) went up 63 mg/dL on average
    • Good cholesterol (HDL) decreased 4 mg/dL on average
    • Similar changes, though not as intense, were observed after 12 months and 24 months
    • Regarding seizures for the curious – After 6 months, 66% of patients had at least 50% less seizures and 17 of those were seizure free.
    • They used a survey given by the staff to see how well the parents and kids were keeping to the keto diets. Results of that survey were not included.



Study #3 – “Negative effect of a low-carbohydrate, high-protein, high-fat diet on small peripheral artery reactivity in patients with increased cardiovascular risk.”


  • Overview and Methods


      • This diet focused on what happens to the lining of your arteries on low-carb and keto diets. This is where the action happens and the damage occurs. Cholesterol, blood pressure, LDL, HDL are all tests used to best guess your rate of heart disease but looking at the arteries themselves is the gold standard.
      • 247 patients were studied
      • A special artery index method was used to put numbers to the relative artery health of each patient.
      • Patients were scored based on the extent to which they followed a particular diet.


  • Key Findings


    • Those on a low-carb, high protein and fat diet had worse artery function and increased heart disease risk.
    • The dieters that were best at keto or low-carb were eating 29% carbs, 24% protein, and 40% fat and had lower small artery function compared to those that had the higher carb diets of scores 45% carb, 20% protein, 32% fat.

Study #4 – “The effect of high-protein diets on coronary blood flow”

See the abstract –

Or read the full PDF study –

  • Overview and Methods
    • Here’s another study that tried to go beyond just looking at cholesterol. They wanted to look deeper at actual blood flow levels. Were arteries getting more clogged on low-carb and keto? That’s what they wanted to find out
    • This study looked at 26 patients, 10 of whom went on a high protein diet that they thought would improve their health. The other 16 went on a diet prescribed by the study.
    • The diet prescribed was simple – 70% carbs, 15% fat, 15% protein. That was the treatment group. The other 10 that chose their own path went on high protein diets.
    • Patients had their major arteries coming out of the heart imaged to look how clogged they were and how well the worked. Typical blood work for cholesterol, blood pressure, and others were also completed.
  • Key Findings
    • High protein group patients didn’t stick to the high protein diet and lost 1% of body weight (1-3 pounds) on average after 12 months
    • Blood flow improved in the treatment group and decreased in the high protein group
    • All patients started with heart disease. It progressed in the high protein group and decreased in the treatment group patients.
    • In the artery images above, notice how the low-fat group arteries opened up whereas the high-protein group didn’t open up as much.

Study #5 – “Modification of Lipoproteins by Very Low-Carbohydrate Diets”

  • Overview and Methods
    • This is another review of studies specifically on low-carb diets. We’ll use it as another shortcut into the research.
    • 40 papers and studies were reviewed to compile these findings
  • Key Findings
    • Low carb diets are bad at reducing LDL cholesterol (the bad kind)
    • Low carb diets are good at increasing HDL cholesterol (the good kind)
    • For those who commit to low carb diets and can maintain weight loss, risk of metabolic disease (leading to diabetes) is reduced
    • Again we find that weight loss is almost more important than the type of type for reducing disease risk and improving heart health

Study #6 – Low-carbohydrate diets and all-cause mortality: a systematic review and meta-analysis of observational studies.

  • Overview and Methods
    • 17 studies were reviewed – Another literature review.
    • 272,000 people were involved in the studies and 15,981 of them died.
  • Key Findings
    • Low-carb dieters had a higher risk of all-cause mortality than other types of dieters; however, it was not linked to cardiovascular disease. They just died more. A larger study specifically comparing low-carb to other diets is needed.

Study #7 – Comparison of effects of high and low carbohydrate diets on plasma lipoproteins and insulin sensitivity in patients with mild NIDDM

  • Overview and Methods
    • Two diets were compared in 1992. Both used the same calories. One was high-carb (60% of calories as carbs) and one was low-carb (35% of calories as carbs). All patients and diabetes but were not insulin dependent.
    • Both diets were low in saturated fat. The low-carb diet was higher in mono-unsaturated fats.
    • Both diets had the same fiber.
    • All patients went on one diet than later switched to the other.
  • Key Findings
    • Glucose and insulin responses didn’t differ significantly between the two diets
    • The high-carb group had worse cholesterol than the low-carb diet. HDL (good cholesterol) decreased and triglycerides and VLDL increased.

Study #8 – A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial

  • Overview and Methods
    • 120 overweight volunteers were compared
    • One set was on a low-carb diet (less than 20 grams of carbs)
    • The other set was on both a low calorie and a low-fat (less than 30% of calories as fats)
    • The study lasted 24 weeks.
  • Key Findings
    • ½ of the low-fat group quit. [Not surprising since they were also calorie restricted].
    • The low-carb group lost twice as much weight as the low-fat group (over 20 lbs lost in low-carb versus 12 pounds in the low-fat)
    • Again we see HDL increase and triglycerides decrease in the low-carb group. These are good changes. No mention was made of total cholesterol changes. LDL (bad cholesterol) didn’t change for either the low-carb or the low-fat groups
    • [Note that again “low-fat” here is defined as 30% of calories. Note that this is more evidence that when you go above 15% calories as fat you don’t get benefits]
    • More “adverse effects” occurred in the low-carb group. What the hell does that mean? I could resist finding out. Here’s the list of adverse effects that the low-carb group complained about more often
      • Constipation
      • Bad breath
      • Headaches
      • Muscle cramps
      • Diarrhea
      • General weakness
      • rashes

Study #9 – Relatively high-protein or ‘lowcarb‘energy-restricted diets for body weight loss and body weight maintenance?

  • Overview and Methods
    • This interesting study wanted to find out if weight loss from low-carb diets was due to the low carbs or due to the higher protein levels
    • 132 volunteers had their weight, fat mass, and blood and urine sample after 3 months and after 12 months.
    • There were on 4 different types of diets
      • Diet 1 – Normal protein-normal carbohydrate
      • Diet 2 – Normal protein-low carb
      • Diet 3 – High protein – normal carb
      • Diet 4 – High protein – low carb
    • Protein intakes were checked for compliance via urine tests every 24 hours – fun!
    • All 4 diets involved calorie restriction with lower calories for the first 3 months and less calorie restriction for the final 9 months
  • Key Findings
    • Body weight and fat mass was reduced after the first 3 months in all diets
    • The high protein-low carb group lost the most weight but all groups lost weight and the differences between groups was only a few pounds.
    • Low-carb versus normal-carb didn’t make much difference for weight loss.
    • High protein lost an extra 8 pounds versus normal protein.
    • High protein – normal carb had the best reductions in blood pressure
    • In general, high protein is more effective than low-carb

Study #10 – Effects of low-carbohydrate and low-fat diets: a randomized trial

  • Overview and Methods
    • Compare low-carb and low-fat diets
    • 148 participants
    • None of the participants had heart disease
    • Low carb was defined as less than 40 grams of carbs a day
    • Low fat was defined as less than 30% of total daily calories as fat [Let’s see them use 15% and see what happens!]
  • Key Findings
    • Most of the low-fat group finished the study. Slightly over half of the low-carb group finished.
    • After 12 months the low-carb group lost over 8 pounds more than the low-fat group
    • Low carb dieters again increased their HDL cholesterol and lowered their triglycerides

Study #11 – Effects of low carbohydrate diets high in red meats or poultry, fish and shellfish on plasma lipids and weight loss

  • Overview and Methods
    • Remember how that first review of studies above recommended not eating red meat if you do low-carb? This one actually compared 2 low-carb diets – one with red meat and one with just chicken and fish.
    • Participants were obese. 18 total were tested.
    • Study lasted 28 days then blood tests were run
  • Key Findings
    • Of the 18 participants, 6 dropped out.
    • Both the red meat and the chicken and fish groups lost 8 lbs on average
    • Final cholesterol readings were very similar between both groups
      • Total cholesterol increased 5 points in both groups
      • LDL increased 3 points in both groups
      • HDL increased about 1.3 points in both groups
      • Triglycerides increased in both groups

Study #12 – Moderate-carbohydrate low-fat versus low-carbohydrate high-fat meal replacements for weight loss

  • Overview and Methods
    • 137 participants
    • 3 groups – control group that did nothing, a low-carb group, and a low-fat group
  • Key Findings
    • The low-fat group had significant reductions in cholesterol
    • Both groups lost weight as well as inches from the waist and thighs

Study #13 – Effects of low-carbohydrate vs low-fat diets on weight loss and cardiovascular risk factors: a meta-analysis of randomized controlled trials

  • Overview and Methods
    • 5 trials with 447 individuals were used in this analysis (i.e. 5 different studies went into this report)
    • Individuals were overweight (body mass index of at least 25)
    • Low-carb was compared to low-fat
  • Key Findings
    • After 6 months more weight was lost in the low-carb group compared to the low-fat group (an additional 6 pounds lost)
    • After 12 months there was no major difference in weight loss between the two groups
    • Again, the low-carb group had improved HDL and triglycerides.
    • The Low-fat group had lower total cholesterol and lower LDL cholesterol (5 point drop)

Study #14 – Low-carbohydrate diets and all-cause and cause-specific mortality: two cohort studies

  • Overview and Methods
    • Study followed participants for over 20 years to see the results of low-carb diets.
    • This started in the 1980s so participants were most likely following Atkins but this isn’t discussed.
    • Over 85,000 women and 44,000 men were followed for 20 or more years as part of this study
    • Low-carb was divided into 2 groups – those that focus on eating more meat and those that focused on eating more plants. Both were low-carb.
  • Key Findings
    • The low-carb group focused on meat had higher all-cause mortality, heart mortality, and cancer mortality
    • The low-carb group focused on plants had lower all-cause, heart, and cancer deaths

Study #15 – Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet

  • Overview and Methods
    • Normal diets compared to Paleo diet
    • 9 non-obese volunteers were part of the study
    • The participants were given their food to help with compliance
    • They started with normal eating and blood tests for 3 days, followed by increased fiber intake, then finally they ate a Paleo diet provided to them for the rest of the study
    • The Paleo diet focused on meat, fruits, vegetables, and nuts. Grains, dairy, legumes were excluded. Some non-paleo items were allowed like mayo and canola oil.
  • Key Findings
    • Blood pressure levels dropped 3 points
    • Total cholesterol dropped 16%
    • LDL cholesterol dropped 22%
    • HDL didn’t change
    • Fasting blood sugar levels didn’t change much

Study #16 – Metabolic and physiologic effects from consuming a hunter-gatherer (Paleolithic)-type diet in type 2 diabetes

  • Overview and Methods
    • 14 Type II diabetics used in the study
    • Compared normal diet to Paleo diet
    • Paleo diet was lean meat, fruits, vegetables and nuts
    • Normal diet was the American Diabetes Association diet
    • Diets were slowly ramped up over 7 days followed by 14 days on the actual diets
  • Key Findings
    • Both groups showed improvements
    • The Paleo group had better glucose control and better cholesterol results
    • The Paleo group had increased insulin sensitivity compared to the ADA group for the patients with the worst insulin sensitivity to start.

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