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By MS Facts in low-fat —

Does a low-fat diet improve MS fatigue?

Does a low-fat diet improve MS fatigue?

Nutrition PhDc Answer: Not based on this study. Energy demands in MS are complex, and not resolved with a dietary change like switching to a low-fat diet. What matters most is making sure that you’re getting food that digests well for you and meets your needs — not adhering to a strict food plan based on someone’s theories and observations.

This is a summary review of a 2023 research article: A low-fat diet improves fatigue in multiple sclerosis: Results from a randomized, controlled trial

Summary: While the title of the study says that a low-fat diet does improve fatigue, the study's results do not fully support that conclusion. When everyone in the study was factored in — those who completed the study and those who quit for any reason — there was no change in fatigue. The study's other limits make it impossible to say that a low-fat diet definitely improves fatigue in MS.

Bottom line: No, this study does not prove that a low-fat diet specifically improves MS-related fatigue. Too many other factors could have been involved. It was also a fairly short diet (12 weeks) and had a small number of participants. The group not doing the diet had some of the same benefits as those who did it, meaning the low-fat study diet wasn’t the reason for some of the positive effects.

Read the full study summary below.

Title: A low-fat diet improves fatigue in multiple sclerosis: Results from a randomized, controlled trial

Type of research: Single-center, two-arm, open-label, randomized controlled trial (RCT)

Length of study: 16 weeks with 12 weeks of actual diet

Number of participants who completed the study: 33 participants (17 in active group, 16 in control group)

Number or percent who dropped out of the study: 6 participants — 3 from each group

Intervention: Low-fat diet (fat less than or equal to 20% of total daily calories, saturated fat less than 7%) versus wait-list control for 12 weeks

Blinding? No (open-label design)

Demographics:

  • Gender: 82% female
  • Race/ethnicity: 85% White; 5% Black; 10% Multiracial
  • Socioeconomic status: Unknown
  • Education: Unknown
  • Other social determinants of health: Not reported

MS Phenotypes:

  • Phenotype: 92% RRMS; 3% SPMS; 5% PPMS
  • EDSS: Average 3.78 (±1.4)

Exclusion(s): Significant depression, diabetes or other medical problems causing fatigue, pregnancy/breastfeeding, MS exacerbation or IV steroids within 30 days of screening, dietary fat content less than 30% at screening, fish/flaxseed oil supplementation within 30 days of screening

Limitations identified by the researchers:

  • Small sample size due to COVID-19 pandemic and inadequate funding
  • Inadequate power to detect impact on fatigue in analysis of all original participants
  • Both groups reduced total calorie intake
  • Active group did not achieve the target of 20% fat calories
  • No data collected on socioeconomic status and education
  • Predominantly white population affecting generalizability
  • Imbalance in fatigue medication use between groups (42% active vs. 16% control)

What were the outcomes?

  • Original study plan with all participants: No significant difference in fatigue between groups (gold standard study outcome)
  • Modified study plan with only those who followed through (possibly biased sample): Significant difference between groups, with the diet group having significantly less fatigue (what the study’s researchers reported in the article headline)

Are we sure the study's intervention directly influenced MS fatigue? No, because a change in food intake could influence energy levels in many ways. It's not definite that the diet change led to fatigue improvements in those who completed the 12-week diet. It could have been eating less, eating foods that were easier to digest (lower-fat ingredients may digest better in some people), or knowing that people were paying attention to their eating habits (the idea of being watched, even by researchers who are only looking at data, could influence eating behaviors).

Are the study's outcomes generalizable to:

  • All people with MS? No. It was 92% RRMS. The study’s authors stated that the results are broadly generalizable because all participants had “moderate-severe disability in at least one functional domain,” but this doesn’t mean the effects translate into all phenotypes or presentations of MS.
  • All disability levels of MS? No. It was mostly lower-disability, with average EDSS of 3.78.
  • All races? No. It was 85% white.
  • All genders? No. It was 82% female.
  • All financial and economic situations? Unknown. Not reported.
  • All educational levels? Unknown. Not reported.

Are there any researcher conflicts of interest? The study did not report any.

Is there any possible researcher bias? Vijayshree Yadav, the study's lead researcher, has studied the McDougall low-fat MS diet for many years. She initially collaborated with McDougall directly and received funding from his foundation to conduct the research. Yadav continues to advocate for a low-fat diet for MS, despite research outcomes not definitively proving it works better for MS than other dietary approaches. Yadav does not appear to have studied other diet types, making it possible that there is a confirmation bias or narrowed lens about possibilities for low-fat diets in MS.